In dealing with the concept of exchange there is frequently a confusion of thought which leads one to speak of a relationship as though it were something external to the elements between which it occurs. Exchange means, however, only a condition of or a change within each of these elements, nothing that is between them in the sense of an object separated in space between the two other objects. … This is just like being misled by the substantive concept of “the kiss” (which to be sure is also “exchanged”) into thinking that a kiss is something that lies outside of the two pairs of lips, outside of their movements and sensations.

Georg Simmel, on individuality and social…, loc. 223