I think that the expression 'the exception proves the rule' used the word 'proves' in the now perhaps archaic sense of 'tests', which makes the meaning of the expression less paradoxical.

Even if they are not so inclined, people should avoid fallacies, roughly because it makes them less likely to acquire new beliefs that are false. But you are not asking what people ought to do, but rather what will in fact lead them to want to avoid fallacies. Maybe we just need to know more about these people to answer this question. Thus perhaps they are inclined to accept pretty much any claim if it is presented in the form of a song, to the tune of 'Happy Days are Here Again'. In that case, I suggest you sing them 'Avoid fallacies, if you can' to that tune. The trouble is that if we try to imagine people who are completely unresponsive to logical force, then who knows what will move them? But actually it's not clear that such a supposition is coherent, because any creature that would count as thinking at all must at least be somewhat responsive to logical force, if their thoughts are to have content. (Of course they may still be prone to various fallacies, and not much bothered by them.)...

In this context, an argument is a set of claims -- the premises -- presented as a reason to accept another claim -- the conclusion. If you are checking for flaws, it is useful to distinguish two fundamentally different ways an argument can go wrong. The first is that one or more or the premises is false or at least unwarranted. The second is that even if all the premises were true, they wouldn't provide a good reason to believe the conclusion. The argument 'Some philosophers are horses therefore some horses are philosophers' suffers from the first flaw (false premise); the argument 'Some people are not philosophers therefore some philosophers are not people' suffers from the second flaw (premise does not provide a good reason for conclusion). When you are checking an argument, consider both types of flaw. Are the premises true? Do they provide good reason for the conclusion? In tackling the second question, it is often a good idea to ask yourself whether, if the premises were all true,...

Many years ago a meteorologist told me that persistence forecasting compares favourably with other, more sophisticated rules for predicting the weather. When I asked the obvious question, she told me that persistence forcasting is the rule that says that the weather tomorrow will be the same as it was today. One thing (though not the first thing) that struck me about this reply was that it does seem perfectly coherent to argue that persistence forecasting is likely to be about as reliable in the future as it was observed to be in the past, even though persistence forecasting is itself a rule that says that that the future will be like the past. If you never checked its track record, you would have no reason to trust persistence forecasting; but if you did, you would. (If you are familiar with the Humean problem of induction, this may suggest to you that it is possible to defend an inductive justification of induction after all. That's what it suggests to me.)

The simplest form of inductive reasoning follows the principle 'more of the same': if we have seen a pattern and have no special reason to think it will change, then we tend to predict that it will stay the same. We have noticed in the past that fire has been hot, so we predict it will be hot in the future too. This form of induction, basic to ordinary life and science alike, seems to operate on a principle of analogy: we are taking it that future events will be analogous to past ones. (Then along comes David Hume, with a devastating argument that we have no non-circular way of showing that the unobserved will be analgous to the observed.) Thomas Kuhn, in his important book The Structure of Scientific Revolutions , brings out another way that analogy is central to science. When scientists choose which new problems to tackle, they are often guided by principles of analogy. They choose problems that seem similar to problems they have already solved, and they apply techniques analagous to...

I'm no Descartes scholar and Jay may well be right that actually Descartes held that God makes the laws of logic true, or neccessarily true. But the answer to the question still seems to be that, for all Descartes knows in the First Meditation (before he has convinced himself of the existence of God), he could be wrong even about those laws, and that would be so even if the laws of logic were beyond the control of God or demon.

I think that once Descartes goes beyond the dream to the demon, we could be wrong about anything. It's not that the demon could change the laws of logic: according to Descartes, I believe, not even God could do that. But the demon could make the simplest logical truths seem false to us and the most blatant logical falsehoods seem true. This is what he calls 'hyperbolic doubt', a beautiful expression for a nasty situation. What is mysterious is how he thinks that even 'cogito ergo sum' can survive this kind of warp-drive skepticism.

If these are arguments which attempt to undermine an opponent's argument by pointing out flaws in her rather than flaws in her reasoning, then the argument against ad hominem arguments is that don't provide good reasons for their conclusions. Rotten people may give sound arguments.

The crucial question is which is more plausible: the premise or the negation of the conclusion. Our answer may be influenced by diverse features of our broader 'web of belief'.

Even if you expect the unexpected, you may still be surprised. I took my Swiss Army knife along, because I expected the unexpected, but I was still surprised when I had to use it to free a hedgehog that got itself locked in the glove compartment of my car. People who believe that life is full of suprises are often right.