determined by the same general causes—viz. demand and supply—as determine the exchange value of other productive services, saved political economy in France from a similar disaster. It was he, also, who furnished Walras with the first outlines of his attractive conception of prices and economic equilibrium. This explains why he never attached to the theory of rent the supreme importance given to it by English economists. In this respect he has been followed by the majority of French economists. On the other hand, and for a similar reason, he never went to the opposite extreme of denying the existence of rent altogether by regarding it merely as the revenue yielded by capital sunk in land. In this way he avoided the error which Carey and Bastiat attempted to defend at a later period.[273] (4) So far it is Say’s brilliant power of logical reasoning that we have admired. But has he contributed anything which is entirely new to the science? His theory of markets was for a long time considered first-class work. “Products are given in exchange for products.” It is a happy phrase, but it is not in truth very profound. It simply gives expression to an idea that was quite familiar to the Physiocrats and to Smith, namely, that money is but an intermediary which is acquired only to be passed on and exchanged for another product. “Once the exchange has been effected it is immediately discovered that products pay for products.”[274] Thus goods constitute a demand for other goods, and the interest of a country that produces much is that other countries should produce at least as much. Say thought that the outcome of this would be the advent of the true brotherhood of man. “The theory of markets will change the whole policy of the world,” said he.[275] He thought that the greater part of the doctrine of Free Trade could be based upon this principle. But to expect so much from such a vague, self-evident formula was to hope for the impossible.