it is the marginal purchase, so it is the marginal purchaser who
matters. It is the man who, before he buys a motor bicycle, weighs the
matter up very carefully indeed and only just decides to buy it, whose
demand affects the price of motor bicycles. It is the utility which
_he_ derives that constitutes the marginal utility, which is roughly
measured by the price.

As to the housewife, I am not prepared to concede that my picture is
in essentials very fanciful. She may be a creature of habits and
instincts like the rest of us, but most habits and instincts affecting
household expenditure are based ultimately on _some_ calculation, if
not one's own, and reason has a way of paying, as it were, periodic
visits of inspection, and pulling our habits and instincts into line,
if they have gone far astray. I am not satisfied that the housewife
does not envisage the utility of a sixth pound of sugar as something
distinct from the utility of the other five; she may buy it, for
example, with the definite object of giving the children some sugar on
their bread, and she may have a very clear idea as to the price which
sugar must not exceed before she will do any such thing. Possibly I
may exaggerate. I have the profound respect of the incorrigibly
wasteful male for the care and skill she displays in laying out her
money to the best advantage.


§5. _The Business Man as Purchaser_. But if the reader still finds the
picture unconvincing, let us shift the scene from domestic economy to
commerce, and substitute for the careful housewife an enterprising
business man. Now, as anyone who has a business man for his father
will have often heard him say, the vagueness and caprice which
characterize our personal expenditure would be quite intolerable in