If we take 'intuition' to mean something like what just seems right or wrong, then philosophy often seems to rely on intuition. One kind of case is when we are trying to analyse a concept. Take the concept of knowledge. We convince ourselves that knowledge is not quite the same as justified true belief, since if you believe that it's 10:45 because your normally reliable watch says so, you don't know it's 10:45 if in fact your watch stopped exactly twelve hours ago, even though your belief is true and justified. But notice that here the argument relies on our intuition that in this case you don't know the time. That seems the right answer, and philosophers lean on that feeling. Another kind of example is a situation in ethics where you decide what is right by playing your intuitions off against each other. It seems right that one shouldn't cause unnecessary suffering, and yet it also seems OK to eat meat. Then you come to believe that eating meat causes unecessary suffering. So for the sake of...

This sounds a lot like Descartes' demon scepticism in the First Meditation. There he worries that he might be mistaken even about things that seem most obvious, like simple mathematical sums. If one suffers from this kind of 'hyperbolic doubt', a doubt that even what seems obviously contradictory might be consistent, and that even what seems obviously consistent might be contradictory, then it is very difficult to see how one could reassure oneself by argument, since one might worry hyperbolically about that very argument. Perhaps if we did suffer from hyperbolic cognitive disability, then we wouldn't even be capable of thought; but that seems cold comfort. Let me make two slightly more encouraging points. The first is that the case for demon scepticism is not as impressive as the case for dream scepticism. For while the dream sceptic can construct a possible world where we are mistaken about the external world, there is a sense in which a demon sceptic cannot even describe the world she is...

I would not say that necessity is defined by our powers of imagination. Maybe some people are better at imagining things that others, but necessity doesn't vary. Like many philosophers these days, I find it helpful to think about necessity instead in terms of 'possible worlds', in terms of different ways the world might be. To say that a statement is necessarily true on this way of thinking about these things is to say that it holds in all possible worlds. Those worlds are not defined by imagination, so neither is necessity. This is not to say that imagination isn't important here, because we use our powers of imagination in order to try to work out whether a statement is or isn't necessary. For example, I may convince myself that something is not necessary because I can imagine it being false. But on this view imagination is a fallible guide to necessity, not the definition of necessity. I might just that something is necessary because I can't imagine it being false, but in fact that's only...

In your scenario, the soul caused an event, but nothing caused the soul. But presumably the cause of the event is some configuration of the soul, perhaps a decision it made. Well was this decision caused or not? If it was caused, then there still doesn't seem to be any free will in the frame; and if that configuration of the soul was uncaused -- just came out of the blue -- then that seems random and again not compatible with free will.

Since 'p' entails 'it is possible that p', the answer to your first question seems to be no. An answer to your second question is that a description says how something is while an explanation says why it is that way. You can think about this in terms of the contrast between knowing that p and understanding why p. Most people know that the same side of the moon always faces the earth; few people understand why.

This doesn't address all of your question, but notice that if (as it seems) we can truly say that certain things do not exist, then there must also be true generalisations, since 'There are no A's' is equivalent to the generalisation that 'Everything is a non-A'. Thus 'Griffins do not exist' is equivalent to 'Everything is a non-griffin', and 'There are no non-black ravens' is equivalent to 'All ravens are black''.

This is not an easy question to answer, in part because it's not clear what it means 'to know what something is'. Still, various sensations may be candidates for things we know better than we can describe, sensations like headaches, the taste of pineapple, or the smell of rotten eggs. The reason is that we know what sensations are like by having them, not by having them described to us. It may seem harder to see how we could know what something like time is better than we can say, since time is not an experience. But there probably are things other than experiences that that we can know better than we can say. For example, I may be better at recognising a person in a crowd than in describing her.

Exactly how 'a priori' should be defined is a delicate matter. Maybe if a newborn were put in a sensory deprivation tank it would never develop the ability to think at all, because the relevant parts of the human brain only develop properly with the help of a reasonably normal course of experience. Would that mean that there is no a priori knowledge? It seems like there might still be an interesting sense in which sentences like 'All bachelors are unmarried' or '2+3=5' are a priori. One proposal is that we distinguish what experience it takes to understand what a sentence means from what it takes to know that it is true. We can then define 'a priori' so that however much experience it takes to understand what a sentence means doesn't count. The question becomes this. Once you understand what a sentence means, do you need additional special experience to know whether it is true? If not, then that sentence can be known a priori. One might try a similar move in answer to your question. ...

It is difficult to see why a zombie couldn't do all the behavioural things we do, and indeed just as efficiently and effectively as we do. But that wouldn't show that consciousness could not arise through evolution, since it might be that we do what we do with the help of consciousness. But maybe consciousness doesn't even help us do what we do: it's just a by-product of the way we do what we do. But even in this case, it might arise through an evolutionary process, just like the lub-dub sound of a beating heart. But suppose now that consciousness does play a causal role in the way we do what we do. Is there any reason why the specific consciousness of ourselves as a free agents might arise through natural selection? Well (and here I am just speculating) maybe a creature that feels in control tends to do better in the world, and that feeling of control leads naturally to an idea of free will, even if it turns out that the idea is ultimately incoherent. This takes us back to the by-product...

Here is another way in which the normative and factual mix in the philosophy of science. One of the central normative issues is whether we are justified in saying that our best scientific theories are (at least approximately) true. The best known argument for saying that our best theories are true is the miracle argument, according to which the truth of our best theories is the only account that avoids making their remarkable predictive successes miraculous. The best known argument for saying that our best theories are not true is the pessimistic induction, according to which the fact that so many of the best theories in the history of science have turned out to be false (even when they were predictively successful at the time) makes it very likely that our current best theories will turn out to be false too. The miracle argument and the pessimistic induction address the normative question of whether we are justified in believing our best theories to be true, and they depend on factual claims about the...