The relativity of value is here made to depend on a ground different from that which lies at the basis of the English School's doctrine of relativity. The ground of the latter is _logical_; the ground for Professor Seligman's view is _psychological_. Values considered as mutual relations between two goods cannot both fall--a fall in one means that it goes lower _than the other_, whence inevitably the other must rise, as a matter of logical definition. For Professor Seligman, on the other hand, value is a quantity of marginal utility. So far as the logic of the situation is concerned, an increase in the supply of good diminishes _their_ marginal utility, and so their value.[189] But, as soon as that is done, a new want springs into existence, a new object receives value therefrom, and the total quantity of value remains as before. In the article from which the quotation is taken, the doctrine is merged to some extent with the English doctrine of logical relativity, as indicated by the discussion on page 343, and by the footnote on page 344. The English doctrine is also suggested by the treatment in the _Principles of Economics_ (pp. 184-85), where it is stated that "prices may rise or fall with reference to this standard, but we cannot speak of a general rise or fall of values, because there is no fixed point." It is clear, however, that the argument for relativity in the passage first quoted, is wholly distinct from, and independent of, the logical relativity of definition. Professor Seligman, in conversation with the writer, has so distinguished it, and has indicated that, rejecting the logical doctrine of relativity, he now holds this psychological doctrine of relativity, as distinct, both from the absolute conception of Professor Clark, and the relative conception of the English School. As preliminary to a criticism of Professor Seligman's doctrine, certain distinctions must be made. Values may be relative in Professor Seligman's sense without being relative in the sense in which the English School uses the term: the English School thought only of the relations among, say, a _unit_ of wheat and a unit of corn, a unit of woolen goods, a unit of wine, etc.: Professor Seligman is thinking of the _total stocks_ of these various commodities. Assume, for simplicity, that the stocks of all commodities were doubled, and that the demand curves for all the commodities have the same shape, and that form is the rectangular hyperbola,[190] so that the absolute value of each unit of each commodity would be exactly cut in half. The English School would say that there had been no change in the values of the units; Professor Seligman would say that there had been no change in the value of the _stocks_, but would concede at once that every unit has had its value cut in half.[191]