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complete satiety—i.e. until its marginal utility has fallen

The supply curve of (B) follows an entirely different course. If the price of (B) is zero, or very low, then there is no inducement for holders of (B) to offer their goods, and when they do begin to do so it will, at first, be only in very small quantities. The supply curve will thus begin at a point on the horizontal axis which is at a certain distance from the origin and will gradually rise pari passu with the rising value of p. But the increase in supply will not continue indefinitely; sooner or later a point will be reached at which an increased price will no longer induce holders of (B) to offer any more, but will, on the contrary, make them offer less, because at this higher price they can obtain with less sacrifice of (B) so much of (A) that its marginal utility will fall until it is equal to the marginal utility of (B), notwithstanding that the latter will also sink when the quantity of (B) retained is increased. The supply curve thus reaches a maximum, from which it falls again towards the horizontal axis ; however, it never cuts the horizontal axis, but moves towards it asymptotically; for however high a price a person is offered for the commodity in his own possession, he will always be prepared to give up some small part of it in order to acquire other goods.1