 Though Bentham did not use this terminology, the calculus he devised—commonly known as the “felicific calculus”—describes the elements or dimensions of the value of a pain or pleasure. To an individual the value of a pain or pleasure will be more or less according to its “intensity”, “duration”, “certainty or uncertainty”, and its “propinquity or remoteness”. Where the object is to measure the value of a pleasure or pain in terms of the tendency of an act, there are two additional circumstances to be taken into account: “fecundity” or “the chance it has of being followed by sensations of the same kind”, and “purity” or “the chance it has of not being followed by sensations of the opposite kind”. Where there are a number of persons, with reference to whom the value of a pleasure or a pain is considered, a further circumstance must be factored into the calculus, that is the “extent” or the number of persons who are affected by the pleasure or pain (1970, 38–39). Although Bentham believed there was nothing in what he had proposed “but what the practice of mankind, wheresoever they have a clear view of their own interest, is perfectly conformable to”, it has often been said that applying the felicific calculus is impractical. Bentham recognised that neither the individual nor the legislator could strictly follow the process he described. Rather, he presented it as a model of the ideal calculation, and “as near as the process actually pursued on these occasions approaches to it, so near will such process approach to the character of an exact one” (1970, 40).