Deductive and inductive arguments

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Zetherin
 
Reply Fri 15 Jan, 2010 04:13 pm
@fast,
fast;120273 wrote:
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.


It's not that Wikipedia pages are poor sources, it's that they are secondary sources.

But any good Wikipedia page is backed by a primary, professional source, generally cited at the bottom. And if the writer does a good job summarizing, Wikipedia pages can be great secondary sources. If you have any genuine criticisms, you should be directing them to the primary sources cited.

In regards to this Wikipedia page, this is the source:

The Fallacy Files Glossary
 
kennethamy
 
Reply Fri 15 Jan, 2010 04:21 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.


In any case, I think it is a good idea to have a term for knowing that the premises and the conclusion are true, when the argument is valid. And "cogent" seems to me an appropriate term for that. So, I have adopted it. Words are important, no doubt, but what they stand for is the thing. After all, "cogent" in this sense, is a neologism. And a term of art. Of course, you need not adopt it for what I do, if you find it somehow inappropriate.
 
Pyrrho
 
Reply Fri 15 Jan, 2010 05:16 pm
@kennethamy,
kennethamy;120270 wrote:
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.


I have seen a logic textbook use the word "cogent" to describe deductive arguments that were such that one had reason to believe that the premises were all true, but that were not necessarily true. Thus, a cogent argument would be one that one would have reason to believe is sound, but if one happened to have been misled about the premises, it may not be.

The main point remains the same, that some terms (such as "valid" when applied to deductive arguments, and "sound") are standard in their meaning, while others are not. When one introduces a term that is not standard, it is a good idea to explain what one means by it, or there is likely going to be unnecessary confusion that follows. The fault in such a case lies with the person who did not explain their nonstandard term, and merely assumed that others would know what they meant by it, as if they were all mind readers or something.

---------- Post added 01-15-2010 at 06:21 PM ----------

fast;120273 wrote:
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.


I looked at a couple of more "professional" sources before using the link to Wikipedia, and they did not use the term "cogent" at all in their discussions of induction. If you are going to introduce nonstandard terms, you should explain their meaning, or at least provide a link to such an explanation. Otherwise, you have no right to complain when someone does not know what you are talking about.
 
fast
 
Reply Fri 15 Jan, 2010 05:24 pm
@Zetherin,
[QUOTE=Zetherin;120279]It's not that Wikipedia pages are poor sources, it's that they are secondary sources.[/QUOTE]I'm not inclined to deny that it's a secondary source, nor would I infer that Wikipedia is a poor source because it's a secondary source. There are other reasons to think it's often a poor source, but this is becoming a tangent.

I gave an argument for what I said, and though I may be mistaken, I need a better rebuttal than being told that what I say is in opposition to Wikipedia. I think Wikipedia is a fine source for giving someone a quick idea of what something is about, but I'd rather see a counter argument or good reason for thinking either I'm mistaken or that Wikipedia is correct.

[QUOTE]If you have any genuine criticisms, you should be directing them to the primary sources cited.[/QUOTE]I don't think I get what you're saying, or at least I hope I don't.


---------- Post added 01-15-2010 at 06:36 PM ----------

Pyrrho;120295 wrote:
I looked at a couple of more "professional" sources before using the link to Wikipedia, and they did not use the term "cogent" at all in their discussions of induction. If you are going to introduce nonstandard terms, you should explain their meaning, or at least provide a link to such an explanation. Otherwise, you have no right to complain when someone does not know what you are talking about.
Well, maybe you should of looked at more sources, like one's that actually address the issue, and why would you think I have introduced a nonstandard term? I wasn't complaining. You were the one telling me that I was wrong. I gave you an argument, and you brought up (of all things) Wiki. Here's a link: I'll find more if you like.

http://www.hu.mtu.edu/~tlockha/h2701n2.s02.doc
 
Zetherin
 
Reply Fri 15 Jan, 2010 07:37 pm
@Emil,
fast wrote:
I think Wikipedia is a fine source for giving someone a quick idea of what something is about, but I'd rather see a counter argument or good reason for thinking either I'm mistaken or that Wikipedia is correct.


But, you see, if the article is cited properly, it isn't about Wikipedia being correct or incorrect. It is about the cited source being correct or incorrect. That is my point.

Wikipedia, often times, is nothing more than a compilation of sources and a summarization of the main points provided in those sources. And, in this case, the source I think you should be criticizing (if you are) is The Fallacy Files Glossary, because that's where what is written on Wikipedia about cogency comes from.

Quote:
I don't think I get what you're saying, or at least I hope I don't.


Well, I hope you begin to get what I'm saying, and I hope you begin to hope you do.
 
fast
 
Reply Fri 15 Jan, 2010 08:30 pm
@Emil,
[INDENT]Cogent
A cogent argument is one such that if the [premises] are true, then the conclusion is more likely to be true than false. Both valid and strong inductive arguments are cogent.
[/INDENT]Can I criticize the author for this, or is this yet another compilation? If it's a compilation, then what's the source for this? Because the way I see it, this isn't anything more than someone throwing darts at hoping to get it right. That's the problem with these second-rate sources. They point us in the right direction, but they don't always get it right. No wonder people who read stuff like this don't know the difference between strong arguments and cogent arguments.

Keep in mind that I'm not claiming to know this material well. I do not need to know the answer to a problem to sometimes recognize an incorrect answer. We have to be careful where we place our confidence.

What is a valid inductive argument anyway?
 
Kielicious
 
Reply Fri 15 Jan, 2010 09:17 pm
@fast,
I dont know if you guys have answered the Op or not but I'll throw out some ideas on the subject.

Deductive arguments have true premises and a conclusion that necessarily follows. While inductive arguments have conclusions that are probable, but not necessary. So me thinks inductive arguments hinge on logical possibility while deductive arguments dont. So its impossible to have a counter example to a deductive argument. Does that work emil?
 
Emil
 
Reply Fri 15 Jan, 2010 09:47 pm
@Emil,
I did not intend for this thread to be about Wikipedia' reliability, so can we please stop discussing that here? I'm willing to discuss it in another thread.

There are so many replies here and many things that I need to correct. Some of you have gotten the picture, so to speak, Ken still holds onto his intention theory but I think I've found some grave problems with it. I will elaborate later. I do not have any theory of the matter.
 
kennethamy
 
Reply Fri 15 Jan, 2010 10:31 pm
@Kielicious,
Kielicious;120357 wrote:
I dont know if you guys have answered the Op or not but I'll throw out some ideas on the subject.

Deductive arguments have true premises and a conclusion that necessarily follows. While inductive arguments have conclusions that are probable, but not necessary. So me thinks inductive arguments hinge on logical possibility while deductive arguments dont. So its impossible to have a counter example to a deductive argument. Does that work emil?



Deductive arguments need not have true premises, and need not have a conclusion that necessarily follows. You can have a deductive argument with false premises, and an invalid deductive argument does not have a conclusion that necessarily follows. Invalid deductive arguments have counterexamples. In fact, that is one way of showing that they are invalid.
 
Emil
 
Reply Fri 15 Jan, 2010 10:34 pm
@Emil,
Pyrrho;120194 wrote:
I am still a bit puzzled by your questions, particularly coming from you. What is wrong with the responses given in a typical introductory logic textbook?


The 'answer' that can be found in a logic textbook is pretty much some vague considerations that seem to stem from the intention theory. But I'm questioning that theory, so this result does clearly not work. This problem is not discussed in any logic textbook that I have read or skimmed through. (I have not read Copi's.)

Pyrrho;120194 wrote:
3. Yes.
4. No, unless you mean that part of a lengthy argument (that is really a series of arguments) is inductive, and part is deductive.


Re 3. Not sure about that. Arguments need to be given. I know that this is a common assumption but is it a good assumption?

Re 4. That's not what I mean.

Also, on further reflection. Skip the second part of question 2 as it is not very relevant here. The discussion about cogent and strong inductive arguments is not what I intended this thread to be about.

When I write "valid" I always mean "deductively valid". I don't think there is a term that is called inductive validity.

Zetherin;120197 wrote:
A deductive argument is an argument where the conclusion follows necessarily from the premises.

A valid deductive argument is a deductive argument where the conclusion follows necessarily from the premises.

A non-valid deductive argument is a deductive argument where the conclusion does not follow necessarily from the premises.


First, your definition of deductive argument is identical with your definition of valid deductive argument. According to you, then, we have no need to speak of valid deductive arguments because all deductive arguments are valid.

Second, you are contradicting yourself. Look at your first and third statement. An invalid deductive argument is according to them both one where the conclusion necessarily follows from the premises and one where it does not. That is impossible.

Also, I dislike that definition of validity very much as it is dangerously ambiguous and causes people to make modal fallacies. There are many logically equivalent definitions of validity. In this thread I stipulate that we use this one:

Validity
[INDENT]An argument is valid iff the corresponding conditional is a necessary true proposition.
[/INDENT]
Zetherin;120197 wrote:
An inductive argument is an argument where the premises offer a degree of support for the conclusion, but do not necessarily entail it; there is no guarentee (like your article noted).


Careful. Do you accept Ken's view (=intention theory)? If so, then some inductive arguments are valid, because some arguments are intended by the speaker to be inductive but are actually valid.

Zetherin;120197 wrote:
I think it depends how we use the word "argument". But, I think if we use the word formally, the answer is yes.


This needs some defending.

Zetherin;120197 wrote:
Do you see how many ways this question can be interpreted?

1.) Yes, some arguments are deductive, some arguments are inductive.
2.) Yes, some arguments (like Pyrrho noted), can have inductive and deductive parts.
3.) No, if you mean that only some arguments are inductive or deductive. Because all formal arguments are deductive or inductive (and you might mean this since this question comes after the one which specifies "all arguments").


Yes, but there is only one good interpretation, and it is straightforward. I even removed extra words that made it even easier to get it right. I suppose I should have left them in. You can insert the word "both" into the question if it is unclear to you, like this:

4. Are some arguments both deductive and inductive?

In the formal english language, E:

4F. Does there exist an argument such that it is deductive and it is inductive?

(I invented some 'formal machinery' (Ken's phrase) for questions to be formalized. In this the question has the form (∃x)(Dx∧Ix)? Let's not discuss this invention in this thread but some other time. The interested reader can look here.)

kennethamy;120199 wrote:
That is not difficult. Deductive arguments are intended to be conclusive arguments by the arguer. If the argument is not conclusive, but is intended to be conclusive, it is a failed (invalid) deductive argument. On the other hand, if an argument is not intended to be a conclusive argument by the arguer, it is non-deductive. But if the premises fail to support the conclusion of the non-deductive argument, then it is a failed (weak) non-deductive argument.

However, whatever the arguer intends, deductive or non-deductive, there are some arguments which it would hardly make sense to intend it as deductive, since it is so clearly non-conclusive; or make sense to intend it as non-deductive since it is so clearly conclusive. It would be a good rule (I think) to count a valid deductive argument as deductive, and a strong non-deductive argument as non-deductive.


This is a good answer from someone defending the standard intention theory. I used to agree with this now I have doubts.

Why do you think it would be a good rule to count a valid argument as deductive even though it is according to that theory inductive?

I assume this is what you meant and you were just being careless when you inserted the word "deductive" there. Otherwise you were merely suggesting that we count valid deductive arguments as deductive. That is not very interesting.

Zetherin;120208 wrote:
But can't we distinguish between inductive and deductive arguments without considering the intent of the arguer at all?


Not according to the intention theory. This implies that the difference between a deductive argument and an inductive argument is merely a psychological one and not a logical one. Some people consider this implausible, me included. See the other threads.

kennethamy;120214 wrote:
I don't see how, although, as I said, there are pretty clear cases of both kind when it would be implausible for the arguer's intention not to be the one or the other. In those cases we have what, in legal jargon, we might call, "constructive intent". That it was the arguer's intent whether or not it actually was (or the arguer was confused).


I agree with this. But even though it is implausible that the arguer intended a given argument to be inductive, it does not follow that it is deductive. Some arguers are terribly confused.

Zetherin;120217 wrote:
But we can distinguish an inductive argument from a deductive argument by looking looking at the argument. If all the premises can be true without the conclusion being true, it is an inductive argument:

1.) Socrates was Greek
2.) Most Greeks eat fish
3.) Socrates ate fish

This is an inductive argument. And we know it's not a deductive argument because although the premises may be true, the conclusion does not follow necessarily from the premises; the conclusion may not be true.

Isn't that right?


Now you have defined inductive argument as invalid argument. That's another theory and it is inconsistent with the intention theory. Let's call this theory for the validity theory, for it defines deductive argument as valid argument, and inductive argument as invalid argument.

This theory has the curious and implausible implication that all deductive arguments are valid, indeed, they could not be invalid. Thus, one cannot fail to make a valid deductive argument, it is impossible. This is the position that Kritikos was defending and to which Ken gave the plausible example arithmetic analogy. See the opening post.

Pyrrho;120220 wrote:
I would rather say, we do not know what the argument is without knowing the intentions of the arguer. But once we know what the argument is, we then may be able to determine whether it is deductively valid or not, and whether it is inductively valid or not.

Perhaps, though, this is a mere verbal distinction, without any importance at all.


Not at all! This is the crucial point. In this post you are endorsing the intention theory. That's fine, but the theory has its problems some of which I have mentioned already.

fast;120229 wrote:
Emil,

I thought what you were meaning to ask for is an analysis of deductive arguments and/or an analysis of inductive arguments. You already know the difference between the two, so you do not need an explanation of what each is. Instead, what you want is an analysis, for merely knowing the difference between the two doesn't therefore imply that you can always be given an argument and definitively determine whether or not the logical argument is a deductive argument or inductive argument, for sometimes, being privy to the argument is insufficient information to determine whether or not an argument is deductive or inductive.

That of course has no bearing on whether or the argument is deductive or inductive, just as truth doesn't depend on knowledge of the truth.

I don't think you should ever regard inductive arguments as valid or invalid.


You are getting the point. I'm not sure that I know the difference between them. I can make the distinction in practice like any person trained in logic can, but that does not imply that I know the difference, does it?

But I am definitely asking for an analysis.

" I don't think you should ever regard inductive arguments as valid or invalid." Why do you think this? Given pretty much any definition that you choose of validity, it is applicable to inductive arguments.

According to the validity theory, all deductive arguments are valid and all inductive arguments are invalid.
According to the intention theory some deductive arguments are valid and some are invalid, and some inductive arguments are valid and some are invalid.

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?


It is nonsense to speak of true/false arguments.

Validity has something to do with form, but not all valid arguments have a valid form. But this is a discussion I would rather not elaborate on now. You can read more about it in Possible Worlds where it is discussed at length.

kennethamy;120236 wrote:
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.


It is also nonsense to say that no arguments are either true or false. The correct wording is:

Zetherin;120239 wrote:
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.


But this is also a side discussion about meaning and category errors. Let's not discuss that now.

kennethamy;120245 wrote:
Right, because premises and conclusions are propositions (statements) and only propositions (statements) are true or false.


Not sure about that. Maybe we should not assume a propositional theory of truth bearers in this thread. Or, better yet, let's assume it so far (pretty much everyone in this thread holds that theory anyway), and maybe after we have considered the problems of deductive and inductive arguments in that light (so to speak), we could consider them in the light of say a sentence theory of truth bearers.

At least, let's not discuss theories of truth bearers in this thread.

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.


You got yourself confused. It is a necessary condition for soundness. But it is not a sufficient. For this thread let's define soundness like this:

Soundness
[INDENT]An argument is sound iff:
1. All the premises and the conclusion are true.
2. The argument is valid.
[/INDENT]
fast;120261 wrote:


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.


This strongness you speak of is not a standard term as far as I know.

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.


I edited the Wikipedia page to its current form (I think). I did it because it was terribly confused before. I also inserted the reference to Fallacyfiles. But bear in mind what Ken says:

kennethamy;120270 wrote:
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.


Correct. I seem to recall writing this on Wikipedia but they may have changed it. Wikipedia is not a good source for such specific information as this.

But let's not derail the thread with more discussions of cogentness and strongness and what have we, that is, terms related to inductive arguments.

fast;120349 wrote:
What is a valid inductive argument anyway?


See the definition of validity above. (And please for the love of god (you do believe in god, right?) stop changing the fonts!)

Kielicious;120357 wrote:
I dont know if you guys have answered the Op or not but I'll throw out some ideas on the subject.

Deductive arguments have true premises and a conclusion that necessarily follows. While inductive arguments have conclusions that are probable, but not necessary. So me thinks inductive arguments hinge on logical possibility while deductive arguments dont. So its impossible to have a counter example to a deductive argument. Does that work emil?


Your first two claims are wrong. I don't know about the rest as they are too vague to consider true or false.
 
fast
 
Reply Fri 15 Jan, 2010 10:53 pm
@Emil,
Emil;120375 wrote:
According to the validity theory, all deductive arguments are valid and all inductive arguments are invalid.
I might agree that inductive arguments are not valid, but from that, I am not inclined to believe that inductive arguments are invalid.
 
kennethamy
 
Reply Fri 15 Jan, 2010 10:56 pm
@Emil,
Emil;120375 wrote:
T

Careful. Do you accept Ken's view (=intention theory)? If so, then some inductive arguments are valid, because some arguments are intended by the speaker to be inductive but are actually valid.



.



I said that if an argument is valid, then we should count it as a deductive argument even if the arguer intends it to be inductive (or thinks it is inductive). Two reasons: 1. It is neater this way. 2. It follows from the principle of charity.
 
Emil
 
Reply Fri 15 Jan, 2010 11:06 pm
@fast,
fast;120378 wrote:
I might agree that inductive arguments are not valid, but from that, I am not inclined to believe that inductive arguments are invalid.


Invalid = not valid.
 
fast
 
Reply Fri 15 Jan, 2010 11:09 pm
@Emil,
Emil;120384 wrote:
Invalid = not valid.

Invalid implies not valid, but not valid doesn't imply invalid, so invalid does not equal not valid.
 
Emil
 
Reply Fri 15 Jan, 2010 11:09 pm
@kennethamy,
kennethamy;120381 wrote:
I said that if an argument is valid, then we should count it as a deductive argument even if the arguer intends it to be inductive (or thinks it is inductive). Two reasons: 1. It is neater this way. 2. It follows from the principle of charity.


This is inconsistent with the intention theory. You would have to make up some clause to remove this inconsistency. I have not found any way to do this.

The principle of charity is only a general maxim that is in general useful to follow.
 
kennethamy
 
Reply Fri 15 Jan, 2010 11:10 pm
@Emil,
Emil;120384 wrote:
Invalid = not valid.


I think fast means that to call inductive arguments invalid is a category mistake. I think that is right.
 
Emil
 
Reply Fri 15 Jan, 2010 11:11 pm
@fast,
fast;120386 wrote:
Invalid implies not valid, but not valid doesn't imply invalid, so invalid does not equal not valid.


Your language use is peculiar. I don't want to discuss this odd view you have about negation suffixes ("-un", "-in" etc.). In this thread "invalid" means "not valid". I stipulate it as I have no patience to go through another case of your (or Ken's) personal language use. (Recall the case with "unjustified" and "not justified"?)

---------- Post added 01-16-2010 at 06:12 AM ----------

kennethamy;120389 wrote:
I think fast means that to call inductive arguments invalid is a category mistake. I think that is right.


It clearly follows from the definition of validity. It is not meaningless either. It clearly means something. That it would be pointless to criticize an inductive argument for being invalid is another thing.
 
kennethamy
 
Reply Fri 15 Jan, 2010 11:13 pm
@Emil,
Emil;120387 wrote:
This is inconsistent with the intention theory. You would have to make up some clause to remove this inconsistency. I have not found any way to do this.

The principle of charity is only a general maxim that is in general useful to follow.


Easy. "except when the argument is valid". That supersedes the intention of the arguer. It is generally useful to follow the principle of charity in this case.
 
Emil
 
Reply Fri 15 Jan, 2010 11:36 pm
@kennethamy,
kennethamy;120392 wrote:
Easy. "except when the argument is valid". That supersedes the intention of the arguer. It is generally useful to follow the principle of charity in this case.


But then the theory is lacking an explanation for this case, otherwise it is special pleading. The theory goes like this:
[INDENT]An argument is inductive iff the arguer intended for it to be inductive, except when it is valid, then it is deductive.
[/INDENT]
Why does the opposite and analogous exception clause not hold too then?:
[INDENT]An argument is deductive iff the arguer intended for it to be deductive, except when it is invalid, then it is inductive.
[/INDENT]Even though it may be useful to see arguments that are intended as inductive, as deductive, they are not deductive according to the definition in that theory. And what is needed is a definition not a general maxim or rule.
 
kennethamy
 
Reply Fri 15 Jan, 2010 11:48 pm
@Emil,
Emil;120400 wrote:
But then the theory is lacking an explanation for this case, otherwise it is special pleading. The theory goes like this: [INDENT]An argument is inductive iff the arguer intended for it to be inductive, except when it is valid, then it is deductive.
[/INDENT]Why does the opposite and analogous exception clause not hold too then?: [INDENT]An argument is deductive iff the arguer intended for it to be deductive, except when it is invalid, then it is inductive.
[/INDENT]Even though it may be useful to see arguments that are intended as inductive, as deductive, they are not deductive according to the definition in that theory. And what is needed is a definition not a general maxim or rule.


Why does the opposite and analogous exception clause not hold too then?: An argument is deductive iff the arguer intended for it to be deductive, except when it is invalid, then it is inductive.

Because that rule would suppose that all inductive arguments are really just failed deductive arguments, and that is not only unintuitive, but it is wrong. I remember one person teaching his class that although the affirming the consequent is fallacious deductively, it is fine inductively, which is an example of this sort of nonsense.

I don't see why, in the interests of neatness and charity, an exception clause cannot be added. As I said before, following the lawyers, we can talk about the argument being "constructively deductive".
 
 

 
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