Trade is a process of finding affinities, and it is, of course, more difficult to find direct affinities than by vicarious process. If one of two traders can give the other an instrument that will ferret out his affinity, it follows that trading may be consummated to a much greater extent than if dependence is had upon the mere chance that two traders can satisfy each other's wants.

This transforms trade from a bilateral to a multilateral operation. To accomplish this transformation is the sole and all important function of money—the ferret of affinities.