It seems to me that there is a quality, which we cannot define but are perfectly well acquainted with, which may be called “Hedonic Tone”. It has the two determinate forms of pleasantness and unpleasantness.
C. D. Broad, Five Types of Ethical Theory, London, 1930, p. 229
If one goes for a long time without serious pain, one can more or less forget its distinctive nature. But then, when it comes, one is reminded only too well of what it is like, that is, of its reality as a distinctive quality of experience.
Timothy Sprigge, ‘Is the esse of Intrinsic Value percipi?: Pleasure, Pain and Value’, in Anthony O’Hear (ed.), Philosophy, the Good, the True and the Beautiful, Cambridge, 2000, p. 127