Since the days of Skinner, associative learning has come in many different variations. But what all varieties should share with their historical predecessors is that associative learning is supposed to mirror the contingencies in the world without adding additional structure to them (see section 9 for some examples of when supposedly associative theories smuggle in extra structure). The question of what contingencies associative learning detects (that is, one’s preferred analysis of what the associative relation R is), is up for debate and changes between theorists.