Hello Everyone,

Informal fallacies have to do with our use and understanding of language, namely the ues of inferance.

Formal fallacies on the other hand are more mathematical in their approach, i.e., if A+B then C.

Andrew, I would say that formal fallicies are mistakes in the form of the argument.  That is to say, they have to do with the shape of the argument irrespective of the meaning of the premises. For example, here is an argument that would be considered valid…

Premise 1: If it rains, then I will get wet.
Premise 2: It rains.
Conclusion: I will get wet.

This argument is formally referred to as Modus Ponens.  Here is the form of the argument…

Premise 1: If A, then B.
Premise 2: A.
Conclusion: B.

Notice, ‘A’ and ‘B’ can stand for any proposition and this remains a valid argument. Why?  Because the form is correct.  It is formally valid.  Now, consider the following argument…

Premise 1: If it rains, then I will get wet.
Premise 2: I will get wet.
Conclusion: It rains.

This argument has the following form…

Premise 1: If A, then B.
Premise 2: B.
Conclusion: A.

This argument is not formally valid.  It is an invalid argument, and would be considered a formal fallacy (asserting the antecedent).  Why?  Because it is not the right form.  Notice, what ‘A’ and ‘B’ mean does not play a part.

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With that said, informal fallacies are fallacies of a different sort, and their nature is not so easy to pin down.  They are fallacies where the meaning of ‘A’ and ‘B’ may play a part - they deal more with the content of what is said.  They deal with such issues as semantics and induction.  I find it easier to study the different arguments that are considered informal fallacies than it is to try to come up with a single definition capturing all informal fallacies.

So, are fallacies of informal fallacies a matter of undistributed middles?

When I speak of the “fallacy of informal fallacies” I am just playing a word game.  Informal fallacies are legitimate fallacies.  My only point was to provide an argument that might be technically considered an informal fallacy that at the same time would be considered by most a reasonable argument (from a practical or psychological point of view).  In other words, the conclusion that the little boy who cried wolf should be ignored is a reasonable conclusion given the boy’s past behavior even though someone might argue that the conclusion commits an informal fallacy. 

Brian

This is where the logic of the slippery slope comes into play.  It is a logical fallacy to say that someone who has committed a “small sin” will commit a “big sin.”
But logic does not account for human nature. 

Human nature is to do something small, and then, when we think we have gotten away with it, something larger. 
The wise will say

It is true that I can drink one beer and not be drunk.  But I know my nature and I know that if I start there is the possibility I might not stop.  If I don’t drink at all, I can not fall down the slippery slope.

So the slippery slope is not a logic rule but a flaw of human nature.  Therefore it is reasonable to avoid the slippery slope.

Andrew

Brian wrote:

Informal fallacies are legitimate fallacies.

So you’re saying that there are such things as logical fallacies? Which means that you can have an error in your logic, but that doesn’t mean that your error isn’t logical?

Tiffany K. wrote:

Brian wrote:

Informal fallacies are legitimate fallacies.

So you’re saying that there are such things as logical fallacies? Which means that you can have an error in your logic, but that doesn’t mean that your error isn’t logical?

Yeah, pretty much.  He’s saying that even though there’s an error, it’s still reasonable.

Interesting… So does it really matter if your error is reasonable or not?

Tiffany K. wrote:

Interesting… So does it really matter if your error is reasonable or not?

First, I’d like to amend my original statement, “He’s saying that even though there’s an error, it’s still reasonable.”  It should read, He’s saying that even though there’s an error, the conclusion is still reasonable.

Second, if your error is reasonable it only matters retrospectively when newer evidence presents itself, or when the after-effects of the conclusion shows; that is, when the rightness or wrongness of the reasonable conclusion can be measured by the effects the conclusion has.

At least, that’s the way I see it.  But maybe I’m in error, reasonably.  Perhaps Brian could present newer evidence…

Cheers!

I think what we are trying to say is that there is more to reason than pure logic alone.  Formal logic is very mathematic in its approach.  If A and B, then always C.  When we deal with real life there is more to it than just A and B and C.

Sometimes what is reasonable isn’t provable.  It is reasonable to assume that some one who is willing to steal 20 dollars is willing to steal 100,000 dollars, but no one can prove it with logic.

Does that make any sense?

Ahh…gotcha. If someone has a reputation of telling the truth, then you can assume that he will tell the truth and be reasonable in that assumption, but you cannot prove that he will do so. Correct?

Tiffany K. wrote:

Ahh…gotcha. If someone has a reputation of telling the truth, then you can assume that he will tell the truth and be reasonable in that assumption, but you cannot prove that he will do so. Correct?

Correct.

Yay! Understanding can be so marvelous!