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 business affairs. There you must weigh and measure with the utmost possible precision. You must be for ever watching the several channels of your expenditure, careful to see that in none does the stream rise higher than the level at which further expenditure ceases to be profitable. You will not even engage typists or install a telephone in your office without weighing up fairly carefully the number of typists or the number of switches that it is worth your while to have. And in deciding whether to employ say, five typists, or six, you will not vaguely lump the services of the whole six typists together, and consider whether as a whole they are worth to you the wages you must give them. You will, in the most direct and literal manner, weigh up the _additional_ benefit you would derive from a sixth typist, and if that does not seem to you equivalent to her wage, you will not engage her, however essential it may be to you to have one or two typists in your office. If on the other hand, the utility of having a sixth typist seems to you worth much more than her pay, the chances are that you will be well advised to consider the employment of a seventh. And so, where you stop employing further typists, the utility to you of the last one, of the "marginal typist" as it were, is unlikely to differ greatly from her pay.