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...

'All statements are false' is necessarily false, so there is at least one true statement.

The past can't change, but what happened in the past affects what will happen in the future. Suppose that you didn't water your plant yesterday. If you believe this, then you will water your plant today and it will be fine. But if you falsely believe that you did water your plant yesterday, then you won't water it today and it will die. So the truth about the past matters.

It's only a rough analogy, but just as the fact that we can see things without understanding how vision works does not remove the interest of a theory of vision, so I would say that the fact that we can know things without understanding the nature of truth does not remove the interest of a theory of truth. Maybe discovering a good theory of truth would not help us discover more ordinary truths, but the fortunately the value of philosophy does not depend entirely on it technological applications.

Philosophers disagree about this, but I think there is such a thing as absolute truth. We need to distinguish the question of truth from the question of knowledge. It may well be there there is no such thing as 'absolutely certain knowledge', something we believe to be true and that we couldn't possibly be wrong about. But whether we can know an absolute truth for certain or not, there could be such a truth. We need to allow that there may be certain statements that are not absolutely true or absolutely false, because they do not have a crisp enough meaning. One way this might happen is if one of the words in the statement is vague. So, it may be that a statement like 'People with exactly 100 hairs on their head are bald' is neither absolutely true nor absolutely false. But it doesn't follow from this that there are no absolute truths, because it doesn't follow that every statement uses vague words. There may be some areas where absolute truth is not to be had. Some people would...

I'm with Richard here: the truth of a proposition cannot be an illusion. In an illusion, the proposition is false. But there might nevertheless be a sense in which truth could be an illusion, if we think that there are representations when in fact there aren't any. This is paradoxical territory, but for example there is a line of thought from Wittgenstein, articulated in Saul Kripke's Wittgenstein on Rules and Private Language , according to which our thoughts do not have determinate content. No determinate content, no determinate proposition, so no truth. If that were the situation, but we thought that there was truth here, we might (truly?) say that truth is an illusion.

Whenever we talk about representations (and philosophers can't stop talking about them), it is important to distinguish between the representations and the things they represent. Representations, such as sentences and thoughts, are human products, but what they represent need not be. You can't think without thinking; it doesn't follow that you can only think about thinking. Still, one might worry that it would be an incredible coincidence if human categories lined up with the categories of the world as it is in itself. But work in the philosophy of language in the last few decades as suggested a way this might not be a coincidence, by showing how the shape of our own categories may in fact be determined by the world's categories. If you would like to follow this idea up, read Saul Kripke's wonderful Naming and Necessity . (And then if you would like to start worrying all over again how the mind could shape categories, read his equally wonderful but more disturbing Wittgenstein on Rules...