"But the 'postulates' of the classical political economy, while restricted and scanty enough, were not as hypothetical or 'assumed' as was supposed by the economists who formulated them. The psychology of the 'economic man,' faulty and unsatisfactory as it was, in the one characteristic essential to the economist above all others was not nearly as remote from reality as his creators supposed. In fact it may almost be said that the 'economic man' was an actual Englishman of the commercial world, the description of whose behavior was correctly obtained by inductive inference from observation, but marred and distorted by faulty deductions from an inaccurate introspective, speculative psychology, in an attempt to obtain a rational explanation of the motivation of his behavior. In his commercial activity, with which the economist is primarily concerned, man is thoroughly economic. As economists we are concerned with his ends and not with his motives. His motives may be numerous enough and complex enough to merit the abstractions of the old economists, but in his ends he is simple enough for inductive investigation. The bottle of medicine for a dying child, or of wine for himself; the tools for his trade; the supplies for a home for the aged, bought as a contribution to the home from a future inmate -- all are bought with the same end of getting the most for the least, whatever the motive for the purchase may be. Nor in asserting that the ordinary individual, in his economic activity, of his possible alternatives follows the one he most desires to follow—which is all the economist need assert -- do we preclude ourselves from the admission that a laborer will not necessarily seek the higher wage if it involves the harder work or the longer day."
Jacob Viner, "Some Problems of Logical Method in Political Economy" (1917)