CAN THERE BE A SUM OF PLEASURES? 377 if we had an hour to give to them would awaken no interest in five minutes. There are books which we do not care to read for less than an hour and others which we should not care to read for so long. Duration, therefore, though an important element in the mensuration of pleasures, does not often practically help us much to an accurate measurement, even where we are dealing with the same external source of enjoyment : and, when we turn to the intensity of pleasures, the want of any satisfactory unit of pleasure is still more obvious. But the difficulty of saying how many units of pleasure there are in a given lot or sum of pleasure does not prevent our arriving to a mental estimate of its quantity and comparing it with the quantity of other pleasures just as an ignorant savage choosing burdens to carry across the Sahara may have very clear ideas of magnitude and weight without any knowledge of inches or pounds. That we make such comparisons and pronounce which of two stretches of consciousness is the most pleasant on the whole, seems to be admitted by some who still object to the term " sum of pleasures". Such persons seem to mean that our estimate of the total pleasure that we shall get from one course of action as compared with what we shall get from another is arrived at without any previous mental addition or summing of pleasures. That we do not, as a rule, con- sciously divide up our prospective pleasure into units, and thus do a sum in arithmetic, I have already admitted. But how we can arrive at an estimate of the amount of a whole without putting together a number of parts is to me unintel- ligible. When I am deciding in which of two ways I shall spend a day or a month devoted to recreation, I certainly do go over in imagination the various hours of the day or the probable occupations of the various days in a month, as it will be spent in each way, and make a rapid estimate (pictur- able in imagination though not actually reduced to terms of any pleasure-unit) of the amount of pleasure which I shall get into each portion of it (though I admit that the portions are not necessarily marked off from each other by exact time- measurements), and then think which comes to the most. If any one tells me he is not conscious of doing so, I should be quite prepared to admit that he really makes such calcu- lations in a less conscious and deliberate way than I am at times conscious of doing myself. Indeed, I believe that the disputes which have arisen on this subject are very largely traceable to differences between the mental habit of individ- uals ; but the idea of a quantity a quantity occupying time which does not consist of parts and is not made up of the
