What are the differences between wrong and ignorant? I guess that you can be ignorant without being wrong, since ignorance may involve having no idea what the answer is. And perhaps you can be wrong without being ignorant, if nobody is in a position to know the right answer, or if say your error is the result of a mistake in a difficult calculation. But maybe the contrast you have in mind is brought out by someone who is ignorant by being wrong in a case where he or she should have known better. Let's go with that. The next challenge is what 'world view' means. Let's suppose that it means some broad philosophical position, like materialism/dualism, realism/anti-realism, realism/nominalism, consequentialism/deontology, etc. In that case, I would say that even if I am convinced that my philosophical position is correct and that yours is therefore wrong, I should not normally say you are ignorant. Big philosophical positions are controversial, they are things over which highly intelligent and...

Different ways of acquiring knowledge doesn't mean that the knowledge acquired is necessarily different. Thus I may know that it is snowing because I see the snow, or because someone tells me, but the knowledge that it is snowing is the same in both cses, even if in one case I have an experience that I don't have in the other. But there may also be different types of knowledge. One apparent difference that philosophers have discussed is between knowing a fact, such as knowing that it is snowing, and having an ability, such as knowing how to ski. These seem like different types of knowledge, though the relationship between them is a subject of some philosophical discussion. (As they say, those that can, do; those that can't, teach.)

The popular dispositional theory of colour that Richard mentions has a curious consequence. If being red is just being such as to tend to produce a certain kind of sensation in us, then it isn't even possible that what tends to look red to us isn't really red but is really say some shade of gray. For on the dispositional view, red just is tending to look red.

This is a tantalizing question. On some subjects I do have a good reason to prefer my own opinions, say because I was there at the time and saw it with my own eyes. But consider philosophical opinions. Why do I bother to form my own opinions? Why don't I just agree with everything Hilary Putnam says, since he is such a good philosopher? That would save me a lot of time, and it might well increase the reliability of my opinions. Well, in the case of philosophy, I guess part of the answer is that we don't just care about maximising the chances of having the right answer: we also think there is a particular value to working things out for oneself. One more point among the many that your question raises. Most of our opinions are not just our own opinions anyway, since almost everything we know we know because of what other people tell us. Philosophers argue over whether reason or experience is the primary source of knowledge; but at a certain level the answer is neither. Testimony or...

As philosophers typically analyze it, knowledge requires belief, truth, and some kind of justification or reliability; but not certainy or the impossibility of doubt. Yet when I tell my wife that I know that the play starts at 8pm and she replies, 'Are you certain?', I find it difficult to reply, 'No, I'm not certain; but I know'.

Knowledge often has practical value, and I would go along with the idea that it sometimes has intrinsic value too: it is good in itself. But I'm not convinced that all knowledge has intrinsic value. For example, I'm not sure that there is even a little intrinsic value to knowing exactly how many hairs I have on my head. So there might be some bits of self-knowledge that are not intrinstically valuable. And I agree with you that there may be some bits of self-knowledge that have negative practical value. For example, knowing about some of one's faults might make them worse. (Knowing how often one tends to stammer might make one stammer even more often.) So it looks like there could be cases of self-knowledge with no instrinsic value and negative practical value.

This is a classic pr0blem in philosophy, the problem of 'spectrum inversion'. Even if you see blue like I see red, and vice versa, it is very difficult to see how we could ever tell. I cannot see your experiences, and you would use the words 'blue' and 'red' the same way I do, since you were taught to say 'blue' when you saw blue objects and 'red' when you saw red objects, even if your experiences were different. It's interested that spectrum inversion is different from color-blindness. There we can tell, because color blind people can make fewer discriminations.

I agree that the sentence "All I know is that I know nothing" is paradoxical, or anyway false, since if there is one thing that you know than you can't know that you know nothing since that isn't true. But we can probably avoid the problem by saying instead "All I know is that I know nothing else".

Ugly carpets don't do much for me, but I'm sympathetic to your thought that there may be knowledge that is carried by non-verbal representations. For example, animals without language can I think nevertheless have perceptual knowledge. Even my old chow chow dog Mishka, not an Einstein even by canine standards, knew when there was food it his bowl.

I don't think so, but I'm not 100% sure about that.