It is an ironic fact that the felt qualities of conscious experience, perhaps the only things that ultimately matter to us, are often relegated in the rest of philosophy to the status of ‘secondary qualities,’ in the shadowy zone between the real and the unreal, or even jettisoned outright as artifacts of confused minds.
Jaegwon Kim, Physicalism, or Something Near Enough, Princeton, 2005, p. 12
I may be wrong in believing that matter exists independently of me. But the suggestion that I am wrong in believing I have a sensation is absurd. The belief is not sufficiently separable from the sensation for the possibility of error. I may, of course, be wrong in believing that I had a sensation in the past, for memory may deceive me. And I may be wrong in the general terms which I apply to a sensation, when I attempt to classify it, and to describe it to others. But my knowledge that I am having the sensation which I am having is one of those ultimate certainties which it is impossible either to prove or to deny.
John McTaggart, Human Immortality and Pre-existence, London, 1916, pp. 26-27