Why should stupidity be painful? Perhaps because stupidity is an evolutionary disadvantage, and evolutionary pressures should have led us to find evolutionary disadvantages painful so we would avoid them. There are lots of problems with this argument. Ill mention just two. First, the mystery seems supposed to be that we have an evolutionary disadvantage -- the non-painfulness of stupidity. But if you are going to be surprised at the existence of an evolutionary disadvantage, why not just be surprised at the existence of stupidity in the first place? Second, there are many disadvantages that are not painful, such as a genetic predisposition to have a fatal but not painful disease. Not everything that is bad for us hurts.

It might also be useful to distinguish the color green from the experience of that colour. Some philosophers (and scientistists, e.g. Galileo) have held that the color just is the experience, but it is m0re common and more plausible to distinguish them. Some would identify the colour with a disposition to produce the experience (which is distinct from experience itself, since it may be present in the dark), some would identify the colour with physical properties of the surfaces of objects, and there are other views as well. Anyway, if colour is say a property of surfaces to reflect light at certain frequencies, then this is something that can be explained to a blind person. But when it comes to the experience itself, it may well be that someone who has not had any visual experience is not in a position to have the full concept of color that the sighted have, and so not in a position to understand the experience as fully as the sighted can.

Disembodied minds may be logically possible, but I think there is no good reason to believe they are actual. It's far more likely (though more boring) that your friend's aunt was imagining those things than that they really exist.

I am innocent of the psychological literature on deja-vu , but one natural hypothesis is that what is happening is that you you have an experience which at the same time gets mis-classified as a memory: the 'memory' isn't actually old, it just seems that way. It's a bit like a forgery, something new made to seem old.

Consider an intense (e.g. sexual) pleasure. I see no reason why some lucky person who had never experiences pain couldn't experience such a pleasure. Even if a person can only enjoy a pleasure by means of some contrast (itself a debatable point), mundane 'neutral' experience is enough of a contrast with intense pleasure: pain is not required. And I would take this one step further: not only could you experience pleasure without having experienced pain, you could experience pleasure even if nobody ever experienced pain.

There seems to be nothing incoherent in the idea that there might be certain people who are much more reliable about the future than the rest of us, though neither we nor they can account for the source of this extraordinary talent. I don't think it is likely that there are any such people about; but if there are this might have an entirely natural explanation (even if we can't quite figure it out). Perhaps they are much more sensitive to sensory evidence and its significance than the rest of us.

Some philosophers think that time is a lot like space: just as all places are equally real even though I am only in one place, so all times are equally real even though I am only in one time. On this view, the fact that the future exists now no more makes it present than the existence of a place over-there makes that place exist here.

This is the ancient and excellent question of how weakness of the will is possible. Alas it seems all too common that we don't do B, which is what we most want to do, because something less important to us -- our desire for A -- gets in the way. On the other hand, if we freely choose to do A rather than B, doesn't that show that we really did want A more after all? Maybe the answer is that we did want A more, but we also wish we wanted B more. But that doesn't account for the feeling that we do sometimes really choose what we want less.

Here is another sort of case. I'm driving in heavy traffic, so I must be thinking about the movement of cars around me, but at the same time I am thinking hard about a philosophical argument. And I'm a safe driver!

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.