The infirmity of this theoretical scheme lies in its postulates, which confine the inquiry to generalisations of the teleological or "deductive" order. These postulates, together with the point of view and logical method that follow from them, the marginal-utility school shares with other economists of the classical line--for this school is but a branch or derivative of the English classical economists of the nineteenth century. The substantial difference between this school and the generality of classical economists lies mainly in the fact that in the marginal-utility economics the common postulates are more consistently adhered to at the same time that they are more neatly defined and their limitations are more adequately realized. Both the classical school in general and its specialized variant, the marginal-utility school, in particular, take as their common point of departure the traditional psychology of the early nineteenth-century hedonists, which is accepted as a matter of course or of common notoriety and is held quite uncritically. The central and well-defined tenet so held is that of the hedonistic calculus. Under the guidance of this tenet and of the other psychological conceptions associated and consonant with it, human conduct is conceived of and interpreted as a rational response to the exigencies of the situation in which mankind is placed; as regards economic conduct it is such a rational and unprejudiced response to the stimulus of anticipated pleasure and pain--being, typically and in the main, a response to the promptings of anticipated pleasure, for the hedonists of the nineteenth century and of the marginal-utility school are in the main of an optimistic temper.[2] Mankind is, on the whole and normally, (conceived to be) clearsighted and farsighted in its appreciation of future sensuous gains and losses, although there may be some (inconsiderable) difference between men in this respect. Men's activities differ, therefore, (inconsiderably) in respect of the alertness of the response and the nicety of adjustment of irksome pain-cost to apprehended future sensuous gain; but, on the whole, no other ground or line or guidance of conduct than this rationalistic calculus falls properly within the cognizance of the economic hedonists. Such a theory can take account of conduct only in so far as it is rational conduct, guided by deliberate and exhaustively intelligent choice--wise adaptation to the demands of the main chance.