Total Posts:38|Showing Posts:1-30|Last Page
Jump to topic:

Deductive Arguments

Envisage
Posts: 3,646
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 8:24:29 AM
Posted: 2 years ago
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop

Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.

Add your favourite syllogisms, have fun!
Envisage
Posts: 3,646
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 8:36:22 AM
Posted: 2 years ago
The other arm of modus tollens are modus ponuns arguments, which I find less useful, but still a valid form of argument they go by the form:

1. If X, then Y
2. X
C. Y

1. If I push tbhidc over a cliff, he will die
2. I pushed tbhidc over a cliff
C. Tbhidc died

What you will more commonly see though is the fallacious denying the antecedent argument:

1. If X, then Y
2. Not X
C. Not Y

1. If I push tbhidc over a cliff, he will die
2. I didn't push tbhidc over a cliff
3. Tbhidc did not die

When of course, there are other conditions which may produce the outcome Y.
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 9:39:52 AM
Posted: 2 years ago
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:

1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.

Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!
Envisage
Posts: 3,646
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 9:48:09 AM
Posted: 2 years ago
At 5/30/2014 9:39:52 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.

Inductive arguments are of a different type of formulation, and they address probability, rather than certainty.

Such as:
Most humans are mortal
Mykeil is a human
Mykeil is probably a mortal


The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:

1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

Modus tollens is deductive...

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.

If I went to the shop I would have also bought sugar as per premise 2, so the objection is self-defeating.

Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

Maybe, the example holds just fine though.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:02:29 AM
Posted: 2 years ago
At 5/30/2014 9:48:09 AM, Envisage wrote:
At 5/30/2014 9:39:52 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.

Inductive arguments are of a different type of formulation, and they address probability, rather than certainty.

Such as:
Most humans are mortal
Mykeil is a human
Mykeil is probably a mortal


That's what valid means. A probability of being true. You just rewarded the distinction I made.


The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:

1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

Modus tollens is deductive...

I've been corrected moden tollens is deductive.


This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.

If I went to the shop I would have also bought sugar as per premise 2, so the objection is self-defeating.

Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

Maybe, the example holds just fine though.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!
Enji
Posts: 1,022
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:08:32 AM
Posted: 2 years ago
At 5/30/2014 10:02:29 AM, Mhykiel wrote:

That's what valid means. A probability of being true. You just rewarded the distinction I made.

No. If an argument is logically valid, then if the conclusion must be true if the premises are true -- not the conclusion is probably true.
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:16:46 AM
Posted: 2 years ago
At 5/30/2014 10:08:32 AM, Enji wrote:
At 5/30/2014 10:02:29 AM, Mhykiel wrote:

That's what valid means. A probability of being true. You just rewarded the distinction I made.

No. If an argument is logically valid, then if the conclusion must be true if the premises are true -- not the conclusion is probably true.

It would be nice if both of you looked up the word "Valid"

Not logically valid or valid argument, but the word itself.

Valid: having a sound basis in logic or fact; reasonable or cogent

notice the words sound, reasonable, cogent.... NONE of those mean certain.
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:21:49 AM
Posted: 2 years ago
Inductive arguments conclude with a "valid" statement. Meaning the conclusion is reasonable and likely or highly probable. Not just that there is a probability or possibility of it being true, but that it is a high chance of it being true.

Deductive arguments conclude with a "certain" or assured statement. The conclusion should follow from the truth of the premises. True premises make it necessary to have the a true conclusion.
Enji
Posts: 1,022
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:31:11 AM
Posted: 2 years ago
At 5/30/2014 10:16:46 AM, Mhykiel wrote:
At 5/30/2014 10:08:32 AM, Enji wrote:
At 5/30/2014 10:02:29 AM, Mhykiel wrote:

That's what valid means. A probability of being true. You just rewarded the distinction I made.

No. If an argument is logically valid, then if the conclusion must be true if the premises are true -- not the conclusion is probably true.

It would be nice if both of you looked up the word "Valid"

Not logically valid or valid argument, but the word itself.

Valid: having a sound basis in logic or fact; reasonable or cogent

notice the words sound, reasonable, cogent.... NONE of those mean certain.

You can't just take a word which has a well defined meaning pertaining to the topic of the thread and then say "but not that meaning." See definition 2b [http://www.merriam-webster.com...]. In logic, an argument is valid if the conclusion necessarily follows from the premises due to the axioms of logic -- 'valid' is an adjective describing the structure of an argument, and it describes deductive arguments. The conclusion of an inductive argument does not necessarily follow from the premises, so valid isn't an adjective used to describe inductive arguments; inductive arguments are instead strong or weak, which reflects the likelihood of the conclusion being true.
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:33:55 AM
Posted: 2 years ago
At 5/30/2014 10:31:11 AM, Enji wrote:
At 5/30/2014 10:16:46 AM, Mhykiel wrote:
At 5/30/2014 10:08:32 AM, Enji wrote:
At 5/30/2014 10:02:29 AM, Mhykiel wrote:

That's what valid means. A probability of being true. You just rewarded the distinction I made.

No. If an argument is logically valid, then if the conclusion must be true if the premises are true -- not the conclusion is probably true.

It would be nice if both of you looked up the word "Valid"

Not logically valid or valid argument, but the word itself.

Valid: having a sound basis in logic or fact; reasonable or cogent

notice the words sound, reasonable, cogent.... NONE of those mean certain.

You can't just take a word which has a well defined meaning pertaining to the topic of the thread and then say "but not that meaning." See definition 2b [http://www.merriam-webster.com...]. In logic, an argument is valid if the conclusion necessarily follows from the premises due to the axioms of logic -- 'valid' is an adjective describing the structure of an argument, and it describes deductive arguments. The conclusion of an inductive argument does not necessarily follow from the premises, so valid isn't an adjective used to describe inductive arguments; inductive arguments are instead strong or weak, which reflects the likelihood of the conclusion being true.

You can not just twist my words around. I was not saying logically valid at all.

I said the conclusion of a inductive argument is valid/invalid.

So Valid is an adjective applied to the word conclusion. Not applied to the word argument.

SO what is the definition of a valid conclusion?. The definition I gave.

Learn to read english.
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:39:55 AM
Posted: 2 years ago
The previous examples are not all deductive arguments. A deductive argument is that if the premises are true the conclusion has to be true. In a deductive argument there is no way for the premises to be true and the conclusion false.

If you look at the previous examples you can see the conclusion could be false or true even if all the premises were true. That makes those examples inductive.

Deductive Arguments:
Modus Ponens:

1. If P, then Q
2. P
3. Therefore Q

1. If the dog is muddy, then the dog will leave muddy footprints
2. the dog is muddy
3. Therefore the dog leaves muddy foot prints.

The conclusion is "definite", "100% certain", or "completely True" IF the premises are true AND X is necessary for Y. You will see this structure often but it is not a deductive argument if X is not necessary for Y. So the relationship between X and Y is one of subsequential, parent-child, cuase-effect.

Modus Tollens:

1. If P, then Q
2. not Q
3. not P

1. If there is a fire detected, then a working fire alarm will buzz.
2.No fire alarm is buzzing
3. No fire detected

Notice with the negative it is like Modus Pollens except now the relationship is inverse. P has to have Q. So if no Q then No P.

Pollens is affirming P
Tollens is negating Q

In Pollens Q requires P to exist.
In Tollens P requires Q for P to exist.
Enji
Posts: 1,022
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:42:06 AM
Posted: 2 years ago
At 5/30/2014 10:33:55 AM, Mhykiel wrote:
At 5/30/2014 10:31:11 AM, Enji wrote:
At 5/30/2014 10:16:46 AM, Mhykiel wrote:
At 5/30/2014 10:08:32 AM, Enji wrote:
At 5/30/2014 10:02:29 AM, Mhykiel wrote:

That's what valid means. A probability of being true. You just rewarded the distinction I made.

No. If an argument is logically valid, then if the conclusion must be true if the premises are true -- not the conclusion is probably true.

It would be nice if both of you looked up the word "Valid"

Not logically valid or valid argument, but the word itself.

Valid: having a sound basis in logic or fact; reasonable or cogent

notice the words sound, reasonable, cogent.... NONE of those mean certain.

You can't just take a word which has a well defined meaning pertaining to the topic of the thread and then say "but not that meaning." See definition 2b [http://www.merriam-webster.com...]. In logic, an argument is valid if the conclusion necessarily follows from the premises due to the axioms of logic -- 'valid' is an adjective describing the structure of an argument, and it describes deductive arguments. The conclusion of an inductive argument does not necessarily follow from the premises, so valid isn't an adjective used to describe inductive arguments; inductive arguments are instead strong or weak, which reflects the likelihood of the conclusion being true.

You can not just twist my words around. I was not saying logically valid at all.

I said the conclusion of a inductive argument is valid/invalid.

So Valid is an adjective applied to the word conclusion. Not applied to the word argument.

SO what is the definition of a valid conclusion?. The definition I gave.

Learn to read english.

A deductive argument is described in terms of validity and soundness. An inductive argument is described in terms of strength and congency. You're using the wrong words.
Envisage
Posts: 3,646
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:47:10 AM
Posted: 2 years ago
At 5/30/2014 10:39:55 AM, Mhykiel wrote:
The previous examples are not all deductive arguments. A deductive argument is that if the premises are true the conclusion has to be true. In a deductive argument there is no way for the premises to be true and the conclusion false.

If you look at the previous examples you can see the conclusion could be false or true even if all the premises were true. That makes those examples inductive.

Deductive Arguments:
Modus Ponens:

1. If P, then Q
2. P
3. Therefore Q

1. If the dog is muddy, then the dog will leave muddy footprints
2. the dog is muddy
3. Therefore the dog leaves muddy foot prints.

The conclusion is "definite", "100% certain", or "completely True" IF the premises are true AND X is necessary for Y. You will see this structure often but it is not a deductive argument if X is not necessary for Y. So the relationship between X and Y is one of subsequential, parent-child, cuase-effect.

Modus Tollens:

1. If P, then Q
2. not Q
3. not P

1. If there is a fire detected, then a working fire alarm will buzz.
2.No fire alarm is buzzing
3. No fire detected

Notice with the negative it is like Modus Pollens except now the relationship is inverse. P has to have Q. So if no Q then No P.

Pollens is affirming P
Tollens is negating Q

In Pollens Q requires P to exist.
In Tollens P requires Q for P to exist.

+1 on Enji, and I didn't give any invalid examples unless I specifically said it was invalid. Such as affirming the consequent or denying the antecedent .
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 10:52:29 AM
Posted: 2 years ago
At 5/30/2014 10:42:06 AM, Enji wrote:
At 5/30/2014 10:33:55 AM, Mhykiel wrote:
At 5/30/2014 10:31:11 AM, Enji wrote:
At 5/30/2014 10:16:46 AM, Mhykiel wrote:
At 5/30/2014 10:08:32 AM, Enji wrote:
At 5/30/2014 10:02:29 AM, Mhykiel wrote:

That's what valid means. A probability of being true. You just rewarded the distinction I made.

No. If an argument is logically valid, then if the conclusion must be true if the premises are true -- not the conclusion is probably true.

It would be nice if both of you looked up the word "Valid"

Not logically valid or valid argument, but the word itself.

Valid: having a sound basis in logic or fact; reasonable or cogent

notice the words sound, reasonable, cogent.... NONE of those mean certain.

You can't just take a word which has a well defined meaning pertaining to the topic of the thread and then say "but not that meaning." See definition 2b [http://www.merriam-webster.com...]. In logic, an argument is valid if the conclusion necessarily follows from the premises due to the axioms of logic -- 'valid' is an adjective describing the structure of an argument, and it describes deductive arguments. The conclusion of an inductive argument does not necessarily follow from the premises, so valid isn't an adjective used to describe inductive arguments; inductive arguments are instead strong or weak, which reflects the likelihood of the conclusion being true.

You can not just twist my words around. I was not saying logically valid at all.

I said the conclusion of a inductive argument is valid/invalid.

So Valid is an adjective applied to the word conclusion. Not applied to the word argument.

SO what is the definition of a valid conclusion?. The definition I gave.

Learn to read english.

A deductive argument is described in terms of validity and soundness. An inductive argument is described in terms of strength and congency. You're using the wrong words.

No you are completely wrong.

A valid argument or a logically valid argument is a description of a sound structure.

a deductive argument leads to a conclusion that is a certainty, fact, true

a inductive leads to a conclusion that is valid, probable, cogent

What I am saying is no different than in every philosophy 101 class. here is just one site out of thousands to help you understand: http://philosophy.lander.edu...
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:03:58 AM
Posted: 2 years ago
At 5/30/2014 8:24:29 AM, Envisage wrote:

Your examples are not deductive. Deductive means the conclusion must be true if the premises are true.

*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the store and bought milk. Therefore not a deductive argument, because the conclusion can be false even if the premise is true.

Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


This only remains logically valid if Y and X are mutually exhaustive or exclusive. The negation of Y does not negate X. In your example you are stating that "not not buying bananas" double negative so positive premise is "buying bananas" negates going to the shop. Which in reality it does not. so not a deductive argument.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.

Add your favorite syllogisms, have fun!

Your examples are erroneous and do not describe a deductive argument because if the premises are true do NOT make your conclusions necessary to follow.
Enji
Posts: 1,022
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:03:59 AM
Posted: 2 years ago
At 5/30/2014 10:52:29 AM, Mhykiel wrote:
At 5/30/2014 10:42:06 AM, Enji wrote:

A deductive argument is described in terms of validity and soundness. An inductive argument is described in terms of strength and congency. You're using the wrong words.

No you are completely wrong.

A valid argument or a logically valid argument is a description of a sound structure.

a deductive argument leads to a conclusion that is a certainty, fact, true

a inductive leads to a conclusion that is valid, probable, cogent

What I am saying is no different than in every philosophy 101 class. here is just one site out of thousands to help you understand: http://philosophy.lander.edu...

Your source doesn't support what you are claiming. It uses validity to describe only deductive arguments, and points out that inductive arguments aren't necessarily deductively valid. Validity, soundness, strength, and cogency are terms which should have been covered in whichever philosophy or logic class you took. Here's the top 3 websites Google found:
http://editthis.info...
http://www.uky.edu...
http://itdc.lbcc.edu...
tbhidc
Posts: 84
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:09:42 AM
Posted: 2 years ago
A valid argument has nothing to do with the truth of the premises. That's completely different. Sure, you could use the word "valid" to mean more likely true than not, but usually "validity" refers to the structure of the argument.

To quote GK Chesterton...

" Logic and truth, as a matter of fact, have very little to do with each other. Logic is concerned merely with the fidelity and accuracy with which a certain process is performed, a process which can be performed with any materials, with any assumption. You can be as logical about griffins and basilisks as about sheep and pigs...Logic, then, is not necessarily an instrument for finding truth; on the contrary, truth is necessarily an instrument for using logic"for using it, that is, for the discovery of further truth and for the profit of humanity. Briefly, you can only find truth with logic if you have already found truth without it."
Envisage
Posts: 3,646
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:10:57 AM
Posted: 2 years ago
At 5/30/2014 11:03:58 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:

Your examples are not deductive. Deductive means the conclusion must be true if the premises are true.

Alright let's see where you think I went wrong.. *rolls sleeves*

*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the store and bought milk. Therefore not a deductive argument, because the conclusion can be false even if the premise is true.

If I went to the shop and bought milk.. I would have also bought sugar, since premise 1 is in play. Therefore I either couldn't not have gone to the sugar and bought milk if I have bought no sugar, or I did buy milk but I also bought sugar, which contradicts the premise 2 I set.

Therefore your objection is just stupid.

Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


This only remains logically valid if Y and X are mutually exhaustive or exclusive. The negation of Y does not negate X. In your example you are stating that "not not buying bananas" double negative so positive premise is "buying bananas" negates going to the shop. Which in reality it does not. so not a deductive argument.

Say what? Premise 1 is still in play, you cannot ignore the premise. If the premises are true then the conclusion necessarily follows. You are claiming I did go to the shop. But if I did go to the shop I would not have bought bananas, but I have. Note that Y is a contingent possibility.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.

Add your favorite syllogisms, have fun!

Your examples are erroneous and do not describe a deductive argument because if the premises are true do NOT make your conclusions necessary to follow.

Yeah.... No.
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:11:45 AM
Posted: 2 years ago
At 5/30/2014 11:03:59 AM, Enji wrote:
At 5/30/2014 10:52:29 AM, Mhykiel wrote:
At 5/30/2014 10:42:06 AM, Enji wrote:

A deductive argument is described in terms of validity and soundness. An inductive argument is described in terms of strength and congency. You're using the wrong words.

No you are completely wrong.

A valid argument or a logically valid argument is a description of a sound structure.

a deductive argument leads to a conclusion that is a certainty, fact, true

a inductive leads to a conclusion that is valid, probable, cogent

What I am saying is no different than in every philosophy 101 class. here is just one site out of thousands to help you understand: http://philosophy.lander.edu...

Your source doesn't support what you are claiming. It uses validity to describe only deductive arguments, and points out that inductive arguments aren't necessarily deductively valid. Validity, soundness, strength, and cogency are terms which should have been covered in whichever philosophy or logic class you took. Here's the top 3 websites Google found:
http://editthis.info...
http://www.uky.edu...
http://itdc.lbcc.edu...

When it says to assess if something is valid it is referring to its structure. Which is to say: is the argument logically valid? Again the term valid I use is in proper respect to being a valid conclusion. I am not using it the sense of it being valid argument.

All the reference you point to are looking at whether the structure of the argument is valid. Which is being used as a synonym for soundness.

A valid conclusion or a Valid answer is a statement that is reasonable, sound, and probable. They follow from inductive reasonings.

A true conclusion or answer, is fact, certain, definite. They follow from deductive reasoning or arguments.

You are confusing what the adjective valid is being applied to. It is an adjective so its definition is applied to the noun it is describing. If you are going to argue semantics you will have to include the noun it is describing to remove the ambiguity. Which I continue to do, but you fail to account for the noun the adjective describes.
tbhidc
Posts: 84
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:12:45 AM
Posted: 2 years ago
At 5/30/2014 9:39:52 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.


The structure of his arguments are still deductive. That's what formal logic is about.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:


No, it's most certainly not.

1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.


Not if the first premise is true. You're just disputing the truth of the premises, not the structure of the argument.

If it's true that whenever I go to the store I buy sugar, then if I didn't buy sugar, I didn't go to the store. The point Envisage is trying to make is about the *structure* of the arguments. Not necessarily the true premises.

Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!
Enji
Posts: 1,022
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:24:45 AM
Posted: 2 years ago
At 5/30/2014 8:24:29 AM, Envisage wrote:

Add your favourite syllogisms, have fun!

P1. Nothing is better than good health.
P2. A hamburger is better than nothing!
C1. A hamburger is better than good health.

Teehee :D
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:25:36 AM
Posted: 2 years ago
At 5/30/2014 11:12:45 AM, tbhidc wrote:
At 5/30/2014 9:39:52 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.


The structure of his arguments are still deductive. That's what formal logic is about.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:


No, it's most certainly not.

I admitted my mistake Modus Tollens is a deductive argument. The examples given are inductive.


1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.


Not if the first premise is true. You're just disputing the truth of the premises, not the structure of the argument.

No. I clearly am stating the conclusion can be false even if the premise is true. That makes it an inductive argument. Because in a deductive argument the conclusion HAS to be true if the premises are true.


If it's true that whenever I go to the store I buy sugar, then if I didn't buy sugar, I didn't go to the store. The point Envisage is trying to make is about the *structure* of the arguments. Not necessarily the true premises.

You added the word "whenever". But even doing so says that the relationship is you always buy sugar when you go to the store. If it was established that you "only" buy sugar when you go to the store than the argument would be deductive. Because buying sugar and going to the store would be a relationship of mutual assurance and negating one would negate the other.


Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!
Envisage
Posts: 3,646
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:26:27 AM
Posted: 2 years ago
At 5/30/2014 11:24:45 AM, Enji wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:

Add your favourite syllogisms, have fun!

P1. Nothing is better than good health.
P2. A hamburger is better than nothing!
C1. A hamburger is better than good health.

Teehee :D

*Universe implodes*
tbhidc
Posts: 84
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:29:45 AM
Posted: 2 years ago
At 5/30/2014 11:25:36 AM, Mhykiel wrote:
At 5/30/2014 11:12:45 AM, tbhidc wrote:
At 5/30/2014 9:39:52 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.


The structure of his arguments are still deductive. That's what formal logic is about.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:


No, it's most certainly not.

I admitted my mistake Modus Tollens is a deductive argument. The examples given are inductive.


1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.


Not if the first premise is true. You're just disputing the truth of the premises, not the structure of the argument.

No. I clearly am stating the conclusion can be false even if the premise is true. That makes it an inductive argument. Because in a deductive argument the conclusion HAS to be true if the premises are true.


If the premises are true, the conclusion HAS to be true. Right. So it's a deductive argument, because if the premises are true the conclusion HAS to be true. That's the *structure* of the argument, not the truth of the statements.

An inductive argument would be like...

Most Americans speak English
You're an American
You speak English

The *structure* is now inductive, since the conclusion draws more than the premises contain.

Whether or not a premise is "more likely true than not" doesn't make something an inductive argument. It's entirely the *structure*. Otherwise, deductive logic would be completely impossible.


If it's true that whenever I go to the store I buy sugar, then if I didn't buy sugar, I didn't go to the store. The point Envisage is trying to make is about the *structure* of the arguments. Not necessarily the true premises.

You added the word "whenever". But even doing so says that the relationship is you always buy sugar when you go to the store. If it was established that you "only" buy sugar when you go to the store than the argument would be deductive. Because buying sugar and going to the store would be a relationship of mutual assurance and negating one would negate the other.


Yes, because the idea is that a modus tollens hypothetical syllogism can be converted into a BARBARA syllogism.

If I argued...

P1: If I go to the store, somtimes I buy sugar
P2: I didn't buy sugar
C: I didn't go to the store

This would be invalid. The "whenever" goes without saying in order to make the argument valid. And obviously, in this example the first premise is false. But the point is to show the *structure* of modus tollens.


Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:30:06 AM
Posted: 2 years ago
At 5/30/2014 11:10:57 AM, Envisage wrote:
At 5/30/2014 11:03:58 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:

Your examples are not deductive. Deductive means the conclusion must be true if the premises are true.

Alright let's see where you think I went wrong.. *rolls sleeves*

*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the store and bought milk. Therefore not a deductive argument, because the conclusion can be false even if the premise is true.

If I went to the shop and bought milk.. I would have also bought sugar, since premise 1 is in play. Therefore I either couldn't not have gone to the sugar and bought milk if I have bought no sugar, or I did buy milk but I also bought sugar, which contradicts the premise 2 I set.

Therefore your objection is just stupid.

the relationship between buying sugar and going the store as you wrote it is neither mutually assurance or mutually exclusive. By offering a scenario in which the premises are true (you did not buy sugar) and the conclusion is false (you went to the store...) I prove it is an inductive argument not deductive. deductive means if the premises are true the conclusion must follow and must be true.


Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


This only remains logically valid if Y and X are mutually exhaustive or exclusive. The negation of Y does not negate X. In your example you are stating that "not not buying bananas" double negative so positive premise is "buying bananas" negates going to the shop. Which in reality it does not. so not a deductive argument.

Say what? Premise 1 is still in play, you cannot ignore the premise. If the premises are true then the conclusion necessarily follows. You are claiming I did go to the shop. But if I did go to the shop I would not have bought bananas, but I have. Note that Y is a contingent possibility.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.

Add your favorite syllogisms, have fun!

Your examples are erroneous and do not describe a deductive argument because if the premises are true do NOT make your conclusions necessary to follow.

Yeah.... No.
Envisage
Posts: 3,646
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:33:38 AM
Posted: 2 years ago
At 5/30/2014 11:30:06 AM, Mhykiel wrote:
At 5/30/2014 11:10:57 AM, Envisage wrote:
At 5/30/2014 11:03:58 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:

Your examples are not deductive. Deductive means the conclusion must be true if the premises are true.

Alright let's see where you think I went wrong.. *rolls sleeves*

*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the store and bought milk. Therefore not a deductive argument, because the conclusion can be false even if the premise is true.

If I went to the shop and bought milk.. I would have also bought sugar, since premise 1 is in play. Therefore I either couldn't not have gone to the sugar and bought milk if I have bought no sugar, or I did buy milk but I also bought sugar, which contradicts the premise 2 I set.

Therefore your objection is just stupid.

the relationship between buying sugar and going the store as you wrote it is neither mutually assurance or mutually exclusive. By offering a scenario in which the premises are true (you did not buy sugar) and the conclusion is false (you went to the store...) I prove it is an inductive argument not deductive. deductive means if the premises are true the conclusion must follow and must be true.

Then you are disputing the soundness of premise 1, and not the validity of the argument, because if I did go to the store, then as per premise 1, I would have bought sugar, regardless of whether or not I bought milk.

I'm sorry but your logic has failed, you might want to play around with these syllogisms some more and it'll become aparent.


Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


This only remains logically valid if Y and X are mutually exhaustive or exclusive. The negation of Y does not negate X. In your example you are stating that "not not buying bananas" double negative so positive premise is "buying bananas" negates going to the shop. Which in reality it does not. so not a deductive argument.

Say what? Premise 1 is still in play, you cannot ignore the premise. If the premises are true then the conclusion necessarily follows. You are claiming I did go to the shop. But if I did go to the shop I would not have bought bananas, but I have. Note that Y is a contingent possibility.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.

Add your favorite syllogisms, have fun!

Your examples are erroneous and do not describe a deductive argument because if the premises are true do NOT make your conclusions necessary to follow.

Yeah.... No.
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:34:28 AM
Posted: 2 years ago
At 5/30/2014 11:29:45 AM, tbhidc wrote:
At 5/30/2014 11:25:36 AM, Mhykiel wrote:
At 5/30/2014 11:12:45 AM, tbhidc wrote:
At 5/30/2014 9:39:52 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.


The structure of his arguments are still deductive. That's what formal logic is about.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:


No, it's most certainly not.

I admitted my mistake Modus Tollens is a deductive argument. The examples given are inductive.


1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.


Not if the first premise is true. You're just disputing the truth of the premises, not the structure of the argument.

No. I clearly am stating the conclusion can be false even if the premise is true. That makes it an inductive argument. Because in a deductive argument the conclusion HAS to be true if the premises are true.


If the premises are true, the conclusion HAS to be true. Right.

ABSOLUTELY

So it's a deductive argument, because if the premises are true the conclusion HAS to be true. That's the *structure* of the argument, not the truth of the statements.

An inductive argument would be like...

Most Americans speak English
You're an American
You speak English

The *structure* is now inductive, since the conclusion draws more than the premises contain.

Whether or not a premise is "more likely true than not" doesn't make something an inductive argument. It's entirely the *structure*. Otherwise, deductive logic would be completely impossible.


The example was:
1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop

Scenerio:

1. I did not buy sugar
2. I went to the store bought milk
3. the premise "I did not buy sugar" is true
4. the conclusion "I did not go to the shop" is false

The true premise did not necessitate the conclusion to be true. Inductive. If it had been written that you "only" go to the store to buy sugar than it would be deductive.

If it's true that whenever I go to the store I buy sugar, then if I didn't buy sugar, I didn't go to the store. The point Envisage is trying to make is about the *structure* of the arguments. Not necessarily the true premises.

You added the word "whenever". But even doing so says that the relationship is you always buy sugar when you go to the store. If it was established that you "only" buy sugar when you go to the store than the argument would be deductive. Because buying sugar and going to the store would be a relationship of mutual assurance and negating one would negate the other.


Yes, because the idea is that a modus tollens hypothetical syllogism can be converted into a BARBARA syllogism.

If I argued...

P1: If I go to the store, somtimes I buy sugar
P2: I didn't buy sugar
C: I didn't go to the store

This would be invalid. The "whenever" goes without saying in order to make the argument valid. And obviously, in this example the first premise is false. But the point is to show the *structure* of modus tollens.


Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:37:02 AM
Posted: 2 years ago
At 5/30/2014 11:33:38 AM, Envisage wrote:
At 5/30/2014 11:30:06 AM, Mhykiel wrote:
At 5/30/2014 11:10:57 AM, Envisage wrote:
At 5/30/2014 11:03:58 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:

Your examples are not deductive. Deductive means the conclusion must be true if the premises are true.

Alright let's see where you think I went wrong.. *rolls sleeves*

*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the store and bought milk. Therefore not a deductive argument, because the conclusion can be false even if the premise is true.

If I went to the shop and bought milk.. I would have also bought sugar, since premise 1 is in play. Therefore I either couldn't not have gone to the sugar and bought milk if I have bought no sugar, or I did buy milk but I also bought sugar, which contradicts the premise 2 I set.

Therefore your objection is just stupid.

the relationship between buying sugar and going the store as you wrote it is neither mutually assurance or mutually exclusive. By offering a scenario in which the premises are true (you did not buy sugar) and the conclusion is false (you went to the store...) I prove it is an inductive argument not deductive. deductive means if the premises are true the conclusion must follow and must be true.

Then you are disputing the soundness of premise 1, and not the validity of the argument, because if I did go to the store, then as per premise 1, I would have bought sugar, regardless of whether or not I bought milk.

I'm not disputing the validity of the argument. I'm disputing you calling it a deductive argument. IS there a scenario in which the premise can be true and the conclusion still false? yes. that means it is not deductive. In a deductive argument if the premises are true the conclusion has to true never false.


I'm sorry but your logic has failed, you might want to play around with these syllogisms some more and it'll become aparent.

I'm trying to help you.



Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


This only remains logically valid if Y and X are mutually exhaustive or exclusive. The negation of Y does not negate X. In your example you are stating that "not not buying bananas" double negative so positive premise is "buying bananas" negates going to the shop. Which in reality it does not. so not a deductive argument.

Say what? Premise 1 is still in play, you cannot ignore the premise. If the premises are true then the conclusion necessarily follows. You are claiming I did go to the shop. But if I did go to the shop I would not have bought bananas, but I have. Note that Y is a contingent possibility.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.

Add your favorite syllogisms, have fun!

Your examples are erroneous and do not describe a deductive argument because if the premises are true do NOT make your conclusions necessary to follow.

Yeah.... No.
tbhidc
Posts: 84
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:39:07 AM
Posted: 2 years ago
At 5/30/2014 11:34:28 AM, Mhykiel wrote:
At 5/30/2014 11:29:45 AM, tbhidc wrote:
At 5/30/2014 11:25:36 AM, Mhykiel wrote:
At 5/30/2014 11:12:45 AM, tbhidc wrote:
At 5/30/2014 9:39:52 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.


The structure of his arguments are still deductive. That's what formal logic is about.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:


No, it's most certainly not.

I admitted my mistake Modus Tollens is a deductive argument. The examples given are inductive.


1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.


Not if the first premise is true. You're just disputing the truth of the premises, not the structure of the argument.

No. I clearly am stating the conclusion can be false even if the premise is true. That makes it an inductive argument. Because in a deductive argument the conclusion HAS to be true if the premises are true.


If the premises are true, the conclusion HAS to be true. Right.

ABSOLUTELY

So it's a deductive argument, because if the premises are true the conclusion HAS to be true. That's the *structure* of the argument, not the truth of the statements.

An inductive argument would be like...

Most Americans speak English
You're an American
You speak English

The *structure* is now inductive, since the conclusion draws more than the premises contain.

Whether or not a premise is "more likely true than not" doesn't make something an inductive argument. It's entirely the *structure*. Otherwise, deductive logic would be completely impossible.


The example was:
1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop

Scenerio:

1. I did not buy sugar
2. I went to the store bought milk
3. the premise "I did not buy sugar" is true
4. the conclusion "I did not go to the shop" is false

The true premise did not necessitate the conclusion to be true. Inductive. If it had been written that you "only" go to the store to buy sugar than it would be deductive.


Because you're looking at only one premise. *Both* premises have to be true for the conclusion to be true. The premise "If I go to the store, then I will buy sugar" is most likely false.

But the structure of the argument is still valid, and it's still a deductively structured argument.

If it's true that whenever I go to the store I buy sugar, then if I didn't buy sugar, I didn't go to the store. The point Envisage is trying to make is about the *structure* of the arguments. Not necessarily the true premises.

You added the word "whenever". But even doing so says that the relationship is you always buy sugar when you go to the store. If it was established that you "only" buy sugar when you go to the store than the argument would be deductive. Because buying sugar and going to the store would be a relationship of mutual assurance and negating one would negate the other.


Yes, because the idea is that a modus tollens hypothetical syllogism can be converted into a BARBARA syllogism.

If I argued...

P1: If I go to the store, somtimes I buy sugar
P2: I didn't buy sugar
C: I didn't go to the store

This would be invalid. The "whenever" goes without saying in order to make the argument valid. And obviously, in this example the first premise is false. But the point is to show the *structure* of modus tollens.


Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!

It seems to me that you're arguing that since we can't know anything for sure, or that we usually use probability to know if a premise is true, then deductive logic is impossible. However, that is false and self-defeating. If we can't do deductive logic, because we can't know whether or not premises are true, what about that premise? How do we know for *sure* that the statement "we can't know whether or not premises are true" is true? If it's true, we can't know it's true. Which is self-defeating, because we're assuming it's true in order to know it's true.

So it seems to me that you're commiting epistemic suicide. Deductive and inductive arguments have to do with the *structure*.

I make the argument

All men are mortal
Socrates is a man
Socrates is mortal

Its deductive. But what if the first premise is only 99.99999% true? I say: So what? It's still deductive. Because whether or not something is deductive or inductive rests solely upon the structure of the argument.
Mhykiel
Posts: 5,987
Add as Friend
Challenge to a Debate
Send a Message
5/30/2014 11:47:42 AM
Posted: 2 years ago
At 5/30/2014 11:39:07 AM, tbhidc wrote:
At 5/30/2014 11:34:28 AM, Mhykiel wrote:
At 5/30/2014 11:29:45 AM, tbhidc wrote:
At 5/30/2014 11:25:36 AM, Mhykiel wrote:
At 5/30/2014 11:12:45 AM, tbhidc wrote:
At 5/30/2014 9:39:52 AM, Mhykiel wrote:
At 5/30/2014 8:24:29 AM, Envisage wrote:
*Disclaimer* tbhidc provided most these examples, I thought I would start something in the forums though which could be collected in a new topic as a stickies thread.

Deductive argument's are really useful for expressing your points simply, in an easy to follow manner and to ensure your case it water-tight. They are also very useful for summarising your opponent's argument so that you may much more easily find the assumptions made and often, the logical fallacies they fail too.


I think your examples are inductive not deductive. Deductive would be a cuase-effect therefore certain true/false. Inductive would be an inference therefore likely valid/invalid.


The structure of his arguments are still deductive. That's what formal logic is about.

The most common one I use myself are modus tollens syllogisms, which run as follows:

1. If X, then Y
2. Not Y
C. Not X


Modeus tollens is inductive. An inductive reasoning can start with a deductive statement. See a deductive arguement is:


No, it's most certainly not.

I admitted my mistake Modus Tollens is a deductive argument. The examples given are inductive.


1. X
2. If X, then Y
3. Y

1. It is sunny outside
2. IF it is sunny outside, THEN I won't have an umbrella.
3. I don't have an umbrella

This example is called denying the consequent, and a verbal example could run as follows:

1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop


You could have gone to the shop and bought milk.


Not if the first premise is true. You're just disputing the truth of the premises, not the structure of the argument.

No. I clearly am stating the conclusion can be false even if the premise is true. That makes it an inductive argument. Because in a deductive argument the conclusion HAS to be true if the premises are true.


If the premises are true, the conclusion HAS to be true. Right.

ABSOLUTELY

So it's a deductive argument, because if the premises are true the conclusion HAS to be true. That's the *structure* of the argument, not the truth of the statements.

An inductive argument would be like...

Most Americans speak English
You're an American
You speak English

The *structure* is now inductive, since the conclusion draws more than the premises contain.

Whether or not a premise is "more likely true than not" doesn't make something an inductive argument. It's entirely the *structure*. Otherwise, deductive logic would be completely impossible.


The example was:
1. If I go to the shop, then I will buy sugar
2. I did not buy sugar
C. I did not go to the shop

Scenerio:

1. I did not buy sugar
2. I went to the store bought milk
3. the premise "I did not buy sugar" is true
4. the conclusion "I did not go to the shop" is false

The true premise did not necessitate the conclusion to be true. Inductive. If it had been written that you "only" go to the store to buy sugar than it would be deductive.


Because you're looking at only one premise. *Both* premises have to be true for the conclusion to be true. The premise "If I go to the store, then I will buy sugar" is most likely false.

But the structure of the argument is still valid, and it's still a deductively structured argument.

I suggest to remove the ambiguity you write "whenever" you go to the store, you "always" buy sugar.


If it's true that whenever I go to the store I buy sugar, then if I didn't buy sugar, I didn't go to the store. The point Envisage is trying to make is about the *structure* of the arguments. Not necessarily the true premises.

You added the word "whenever". But even doing so says that the relationship is you always buy sugar when you go to the store. If it was established that you "only" buy sugar when you go to the store than the argument would be deductive. Because buying sugar and going to the store would be a relationship of mutual assurance and negating one would negate the other.


Yes, because the idea is that a modus tollens hypothetical syllogism can be converted into a BARBARA syllogism.

If I argued...

P1: If I go to the store, somtimes I buy sugar
P2: I didn't buy sugar
C: I didn't go to the store

This would be invalid. The "whenever" goes without saying in order to make the argument valid. And obviously, in this example the first premise is false. But the point is to show the *structure* of modus tollens.


Substituting Y for a negative, is also logically valid, and falls into the same category.

1. If X, then not Y
2. Y
C. X

1. If I go to the shop, I will not buy bananas
2. Bananas were bought
C. I did not go to the shop


I think you made a grammatical error some where.

A common fallacy you will see in debates though, is one called 'Affirming the Concequent'

Which is as follows:

1. If X, then Y
2. Y
C. X

1. If I go to the shop, I will buy bananas
2. I bought bananas
C. I went to the shop

The problem when written verbally should be quite apparent, there could be other situations in which Y could have been fulfilled, such as going to a market, or a fruit salesman.


You demonstrated the fallacy earlier in the thread when you gave an example of a watertight deductive argument.

Add your favourite syllogisms, have fun!

It seems to me that you're arguing that since we can't know anything for sure, or that we usually use probability to know if a premise is true, then deductive logic is impossible. However, that is false and self-defeating. If we can't do deductive logic, because we can't know whether or not premises are true, what about that premise? How do we know for *sure* that the statement "we can't know whether or not premises are true" is true? If it's true, we can't know it's true. Which is self-defeating, because we're assuming it's true in order to know it's true.

So it seems to me that you're commiting epistemic suicide. Deductive and inductive arguments have to do with the *structure*.

I make the argument

All men are mortal
Socrates is a man
Socrates is mortal

Its deductive. But what if the first premise is only 99.99999% true? I say: So what? It's still deductive. Because whether or not something is deductive or inductive rests solely upon the structure of the argument.