But secondly, granting that each of our pleasures and pains has really a definite degree of pleasantness or painfulness, the question still remains whether we have any means of accurately measuring these degrees. Is there any reason to suppose that the mind is ever in such a state as to be a perfectly neutral and colourless medium for imagining all kinds of pleasures? Experience certainly shows us the frequent occurrence of moods in which we have an apparent bias for or against a particular kind of feeling. Is it not probable that there is always some bias of this kind? that we are always more in tune for some pleasures, more sensitive to some pains, than we are to others? It must, I think, be admitted that the exact cognition of the place of each kind of feeling in a scale of desirability, measured positively and negatively from a zero of perfect indifference, is at best an ideal to which we can never tell how closely we approximate. Still in the variations of our judgment and the disappointment of our expectations we have experience of errors of which we can trace the causes and allow for them, at least roughly; correcting in thought the defects of imagination. And since what we require for practical guidance is to estimate not individual past experiences, but the value of a kind of pleasure or pain, as obtained under certain circumstances or conditions; we can to some extent diminish the chance of error in this estimate by making a number of observations and imaginative comparisons, at different times and in different moods. In so far as these agree we may legitimately feel an increased confidence in the result: and in so far as they differ, we can at least reduce our possible error by striking an average of the different estimates. It will be evident, however, that such a method as this cannot be expected to yield more than a rough approximation to the supposed truth.
§ 7. We must conclude then that our estimate of the hedonistic value of any past pleasure or pain, is liable to an amount of error which we cannot calculate exactly; because the represented pleasantness of different feelings fluctuates and varies indefinitely with changes in the actual condition of the representing mind. We have now to observe that, for similar reasons, even supposing we could adequately allow for, and so exclude, this source of error in our comparison of past pleasures, it is liable to intrude again in arguing from the past to the future. For our capacity for particular pleasures may be about to change, or may have actually changed since the experiences that form the data of our calculation. We may have reached the point of satiety in respect of some of our past pleasures, or otherwise lost our susceptibility to them, owing to latent changes in our constitution: or we may have increased our susceptibility to pains inevitably connected with them: or altered conditions of life may have generated in us new desires and aversions, and given relative importance to new sources of happiness. Or any or all of these changes may be expected to occur, before the completion of the course of conduct upon which we are now deciding. The most careful estimate of a girl’s pleasures (supposing a girl gifted with the abnormal habit of reflection that would be necessary) would not much profit a young woman: and the hedonistic calculations of youth require modification as we advance in years.