Deduction and induction

[Speakpigeon]

The technical term, "valid" applies only to deductive arguments, and there is no technical term, "valid" that applies to non-deductive arguments. An inductive argument is a kind of non-deductive argument;moreover, there is no technical term, "valid" that applies to inductive arguments. So, if there is a term, "valid" that applies to inductive arguments (and I concede to the claim there are), then the term is not a technical term. By technical term, I mean a kind of stipulative term.

Of course this is a philosophy forum not a tutorial on logic so there's no reason why we should restrict ourselves to technical terms, be they those used by logicians or philosophers.

If a conclusion to an argument MUST follow from its premises (be it true or not), then 1) the argument is deductive and 2) the form of the argument is valid (and I'm using the technical meaning of the word, "valid"; hence, I'm not using the lexical meaning of the word.

I'm not sure where you picked up this expression "must follow" but I hope it's not standard usage. A conclusion follows or does not follow from the premises, it never must follow. In a valid deductive argument, the conclusion is said to follow from the premises and, conversely, if the conclusion of a deductive argument follows from the premises then the argument is said to be valid.
EB

 

[fast]

Of course this is a philosophy forum not a tutorial on logic so there's no reason why we should restrict ourselves to technical terms, be they those used by logicians or philosophers.

If a conclusion to an argument MUST follow from its premises (be it true or not), then 1) the argument is deductive and 2) the form of the argument is valid (and I'm using the technical meaning of the word, "valid"; hence, I'm not using the lexical meaning of the word.

I'm not sure where you picked up this expression "must follow" but I hope it's not standard usage. A conclusion follows or does not follow from the premises, it never must follow. In a valid deductive argument, the conclusion is said to follow from the premises and, conversely, if the conclusion of a deductive argument follows from the premises then the argument is said to be valid.
EB

But that's just it. That's the heart of the matter, and that's why inductive arguments aren't valid. Validity begets necessity. If an argument is sound, the conclusion must be true.

Although now that I think about it, I don't mean to suggest something that I think I am suggesting. Grrr. Gotta think about something.

 

[Speakpigeon]

But that's just it. That's the heart of the matter, and that's why inductive arguments aren't valid. Validity begets necessity. If an argument is sound, the conclusion must be true.

I'm sure I didn't say or suggest that the conclusion of a valid deductive argument is not necessarily true when the premises are true. The term "follow" already expresses the idea of conditional necessity. No need to qualify "follow" with a "must". The conclusion mustn't follow. It just follows, or it doesn't. If it follows, using "must" is a confusion.
EB

 

[fast]

But that's just it. That's the heart of the matter, and that's why inductive arguments aren't valid. Validity begets necessity. If an argument is sound, the conclusion must be true.

I'm sure I didn't say or suggest that the conclusion of a valid deductive argument is not necessarily true when the premises are true. The term "follow" already expresses the idea of conditional necessity. No need to qualify "follow" with a "must". The conclusion mustn't follow. It just follows, or it doesn't. If it follows, using "must" is a confusion.
EB

That comes across as contradictory.

 

[Philos]

I think we actually agree.

Actually, I'm quite sure we don't, at least judging on what you said in your post. However, I already explained in my few recent posts all that you would need to know to understand why and I don't want to reiterate.
EB

Speakpigeon,

Agreed. I'm not sure that we can agree if (as you claim) I don't understand what you are talking about. Of course that is a different philosophical point and food for another long and interesting thread.

Alex.

 

[fast]

I'm sure I didn't say or suggest that the conclusion of a valid deductive argument is not necessarily true when the premises are true. The term "follow" already expresses the idea of conditional necessity. No need to qualify "follow" with a "must". The conclusion mustn't follow. It just follows, or it doesn't. If it follows, using "must" is a confusion.
EB

That comes across as contradictory.

I did not know that "follow" expresses the idea of conditional necessity. Thank you.

 

[Speakpigeon]

I did not know that "follow" expresses the idea of conditional necessity. Thank you.

I'm not sure what it could possibly express if not that. Perhaps that q comes after p in writing a p->q implication? That the truth value of q follows that of p? Something else?
EB

 

[Speakpigeon]

Actually, I'm quite sure we don't, at least judging on what you said in your post. However, I already explained in my few recent posts all that you would need to know to understand why and I don't want to reiterate.
EB

Agreed. I'm not sure that we can agree if (as you claim) I don't understand what you are talking about. Of course that is a different philosophical point and food for another long and interesting thread.

But I didn't claim you didn't understand my posts. I didn't even suggest it. Maybe you didn't understand but there are alternatives so you can't even make the inference from what I said.
EB

 

[Philos]

Maybe you didn't understand but there are alternatives so you can't even make the inference from what I said.
EB

Speakpigeon,

Yes, If I didn't understand you I couldn't make any inference from what you said. I might be able to make other inferences but I couldn't make inferences from the remarks you made which I didn't understand.

Alex.

 

[StarryNight]

The validity of induction is an old conundrum of philosophy. Everybody accepts the validity of deduction, so how does induction fit in? If one treats induction as a kind of deduction, one finds it to be a fallacy, Affirming the Consequent alongside Denying the Antecedent. Or at least so it seems at first sight.

I once saw the counterargument that one's experience validates induction, but that is itself an inductive argument.

Has anyone gotten anywhere on this question?

Well inductive reasoning, by definition, is contingent. Its answers and conclusions are probably true, but by implication also probably false. Therefore in at least one "possible world" (conceivable, logically coherent set of circumstances) inductive reasoning fails. What the problem seems to specify is that it be justified (known to be reliable) unfailingly, in all possible circumstances, but that would therefore be a contradiction in terms. So asking for a unfailing justification is QED to be inconsistent, like asking for a me to produce a square triangle, or "grue"...

 

[Trodon]

Can you give an example of what you see as a typical inductive argument?

Since 1900, the Dow has averaged a 7.8% annual gain under Democratic presidents, compared with a 3% annual gain under Republicans.
http://blogs.wsj.com/marketbeat/2012/11/06/what-an-obama-win-may-mean-for-stocks/

Therefore Democratic economic policies are more congenial to a bull market than Republican economic policies.

--------

This is not a deductive argument, because factors unrelated to Democratic economic policies may contribute to a good stock market when we have Democrat presidents.

A deductive argument would be:

all presidents of the United States have been American citizens;

Barack Obama is the President of the United States;

therefore Barack Obama is an American citizen.