Deductive and inductive arguments

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fast
 
Reply Fri 15 Jan, 2010 02:23 pm
@Emil,
yeah
.........................
 
kennethamy
 
Reply Fri 15 Jan, 2010 02:27 pm
@Zetherin,
Zetherin;120231 wrote:
I got soundness and validity confused. Validity speaks nothing of truth, only form. To be valid means that the conclusion follows from the premises. An argument being valid does not mean that it is true. Validity is a necessary but not sufficient condition for soundness. It is not a sufficient condition because an argument not only needs to be valid to be sound, but it also needs to be true.

Is this right?


No arguments are either true or false. Are you, perhaps asking whether a valid argument must have a true conclusion. The answer is, no. The same for whether a valid argument must have true premises. But, what is true is that any valid argument with true premises must have a true conclusion.
 
Zetherin
 
Reply Fri 15 Jan, 2010 02:31 pm
@Emil,
kennethamy wrote:

Are you, perhaps asking whether a valid argument must have a true conclusion. The answer is, no.


No, I'm not asking that. I just told you explicitly the opposite. See here:

Quote:

An argument being valid does not mean that it is true


Quote:

But, what is true is that any valid argument with true premises must have a true conclusion.


Right. Gotcha.

Quote:

No arguments are either true or false.


Ah, arguments cannot be said to be true or false, just valid or sound, right? Premises and conclusions are what we apply the properties true and false to.
 
fast
 
Reply Fri 15 Jan, 2010 02:32 pm
@Emil,
My yeah still applies to what he said before he edited.
 
Zetherin
 
Reply Fri 15 Jan, 2010 02:33 pm
@fast,
fast;120240 wrote:
My yeah still applies to what he said before he edited.


So you disagree with this? (this is the part I edited in)

Zetherin wrote:

Validity is a necessary but not sufficient condition for soundness. It is not a sufficient condition because an argument not only needs to be valid to be sound, but it also needs to be true.
 
fast
 
Reply Fri 15 Jan, 2010 02:37 pm
@Zetherin,
We use the terms, "valid", "invalid", "sound," and "unsound" to describe deductive arguments.

We use the terms, "weak," "strong", "cogent", and "not cogent" to describe inductive arguments.
 
kennethamy
 
Reply Fri 15 Jan, 2010 02:37 pm
@Zetherin,
Zetherin;120239 wrote:
No, I'm not asking that. I just told you explicitly the opposite. See here:





Right. Gotcha.



Ah, arguments cannot be said to be true or false, just valid or sound, right? Premises and conclusions are what we apply the properties true and false to.


Right, because premises and conclusions are propositions (statements) and only propositions (statements) are true or false.
 
fast
 
Reply Fri 15 Jan, 2010 02:38 pm
@Zetherin,
Zetherin;120241 wrote:
So you disagree with this? (this is the part I edited in)
As I recall, I agreed with everything you said before you edited. He is right; arguments are not true or false.
 
Zetherin
 
Reply Fri 15 Jan, 2010 02:40 pm
@fast,
fast;120246 wrote:
As I recall, I agreed with everything you said before you edited. He is right; arguments are not true or false.


Oh, I see now. What I meant to say is that the premises and conclusion within the argument have to be true.
 
kennethamy
 
Reply Fri 15 Jan, 2010 02:44 pm
@Zetherin,
Zetherin;120247 wrote:
Oh, I see now. What I meant to say is that the premises and conclusion within the argument have to be true.


Why would that be? Have to be true so that what? All the statements in the argument may be true, and the argument may be either valid, or invalid.
 
Zetherin
 
Reply Fri 15 Jan, 2010 02:45 pm
@kennethamy,
kennethamy;120248 wrote:
Why would that be? Have to be true so that what? All the statements in the argument may be true, and the argument may be either valid, or invalid.


I was speaking about soundness.

Validity is a necessary but not sufficient condition for soundness. It is not a sufficient condition because an argument not only needs to be valid to be sound, but the premises and conclusion within the argument also need to be true.
 
kennethamy
 
Reply Fri 15 Jan, 2010 02:51 pm
@Zetherin,
Zetherin;120249 wrote:
I was speaking about soundness.

Validity is a necessary but not sufficient condition for soundness. It is not a sufficient condition because an argument not only needs to be valid to be sound, but the premises and conclusion within the argument also need to be true.


A necessary condition for a sound argument is not that the conclusion be true, although, if an argument is sound, then the conclusion will be true. Truth, then, is a consequent of soundness.
 
fast
 
Reply Fri 15 Jan, 2010 02:52 pm
@Zetherin,
[QUOTE=Zetherin;120249]I was speaking about soundness.

Validity is a necessary but not sufficient condition for soundness. It is not a sufficient condition because an argument not only needs to be valid to be sound, but the premises and conclusion within the argument also need to be true.[/QUOTE]Yes, but I wouldn't add "and conclusion." An argument is sound if 1) it's valid and 2) all premises are true. There are no sound arguments with false conclusions.
 
Zetherin
 
Reply Fri 15 Jan, 2010 02:55 pm
@kennethamy,
kennethamy;120250 wrote:
A necessary condition for a sound argument is not that the conclusion be true, although, if an argument is sound, then the conclusion will be true. Truth, then, is a consequent of soundness.


But an argument cannot be sound unless it has true premises and a true conclusion, right? So wouldn't that make the truth of the premises and conclusion a necessary condition for an argument to be sound?

There are no sound arguments with false conclusions, are there?
 
Pyrrho
 
Reply Fri 15 Jan, 2010 03:05 pm
@fast,
fast;120243 wrote:
We use the terms, "valid", "invalid", "sound," and "unsound" to describe deductive arguments.

We use the terms, "weak," "strong", "cogent", and "not cogent" to describe inductive arguments.


Who are "we"? But more seriously, the terms for induction are not standardized, and the terms do not line up between deductive and inductive arguments (i.e., although "valid" may be analogous to "cogent", there is no analog for soundness in induction, at least among the terms you have used, according to the links below).

From looking at:

Inductive reasoning - Wikipedia, the free encyclopedia

Cogency - Wikipedia, the free encyclopedia

It would appear that "cogent" and "strong" mean the same thing, and, presumably, "weak" and "not cogent" would also mean the same thing.

---------- Post added 01-15-2010 at 04:11 PM ----------

Zetherin;120231 wrote:
I got soundness and validity confused. Validity speaks nothing of truth, only form. To be valid means that the conclusion follows from the premises. An argument being valid does not mean that it is true. [emphasis added] Validity is a necessary but not sufficient condition for soundness. It is not a sufficient condition because an argument not only needs to be valid to be sound, but it also needs to be true. [emphasis added]

Is this right?


Not quite, though I think what you might mean is correct. Statements are things that may be true or false, not arguments. Arguments may be valid or invalid, sound or unsound. You appear to have the right idea about valid (though your formulation seems a bit ambiguous). To be sound means that the argument is deductively valid and all of its premises are true. Thus, its conclusion will be true, because, to be valid, the conclusion must follow from the premises.

I think people have gotten confused about what you mean because of your statements about arguments being true, which is not a good way of speaking.
 
Zetherin
 
Reply Fri 15 Jan, 2010 03:19 pm
@Emil,
Pyrrho wrote:

I think people have gotten confused about what you mean because of your statements about arguments being true, which is not a good way of speaking.


I believe you are correct. Thanks for the clarifications, and I agree with all you have written.
 
fast
 
Reply Fri 15 Jan, 2010 03:23 pm
@Pyrrho,
[QUOTE=Pyrrho;120255]It would appear that "cogent" and "strong" mean the same thing, [...]. [/quote]

All cogent arguments are strong arguments, but not all strong arguments are cogent arguments, for all cogent arguments are strong arguments with true premises, and not all strong arguments have true premises.
 
Pyrrho
 
Reply Fri 15 Jan, 2010 03:28 pm
@fast,
fast;120261 wrote:
Pyrrho;120255 wrote:
It would appear that "cogent" and "strong" mean the same thing, [...].
All cogent arguments are strong arguments, but not all strong arguments are cogent arguments, for all cogent arguments are strong arguments with true premises, and not all strong arguments have true premises.


That is not what it says at Wikipedia:

Quote:
An argument is cogent if and only if the truth of the argument's premises would render the truth of the conclusion probable.


Cogency - Wikipedia, the free encyclopedia

You may use the term differently, but this only reinforces my point that the terms used to describe various inductive arguments are not very standardized.
 
kennethamy
 
Reply Fri 15 Jan, 2010 03:59 pm
@Pyrrho,
Pyrrho;120255 wrote:
Who are "we"? But more seriously, the terms for induction are not standardized, and the terms do not line up between deductive and inductive arguments (i.e., although "valid" may be analogous to "cogent", there is no analog for soundness in induction, at least among the terms you have used, according to the links below).

From looking at:

Inductive reasoning - Wikipedia, the free encyclopedia

Cogency - Wikipedia, the free encyclopedia

It would appear that "cogent" and "strong" mean the same thing, and, presumably, "weak" and "not cogent" would also mean the same thing.

---------- Post added 01-15-2010 at 04:11 PM ----------



Not quite, though I think what you might mean is correct. Statements are things that may be true or false, not arguments. Arguments may be valid or invalid, sound or unsound. You appear to have the right idea about valid (though your formulation seems a bit ambiguous). To be sound means that the argument is deductively valid and all of its premises are true. Thus, its conclusion will be true, because, to be valid, the conclusion must follow from the premises.

I think people have gotten confused about what you mean because of your statements about arguments being true, which is not a good way of speaking.


Actually, some logic books use the term "cogent" to mean, "known to be true", and not just true. So, a cogent argument would be one where the premises are not only true (and argument valid) but are known to be true, so the conclusion is known to be true. But the books differ on this.
 
fast
 
Reply Fri 15 Jan, 2010 04:02 pm
@Pyrrho,
Pyrrho;120263 wrote:
That is not what it says at Wikipedia:

Cogency - Wikipedia, the free encyclopedia

You may use the term differently, but this only reinforces my point that the terms used to describe various inductive arguments are not very standardized.

Consider your source. You are not using a professional source. You are using an inferior source. I have heard Emil talk good of Wikipedia, but it's still a poor source.
 
 

 
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