In one of its senses, “associationism” refers to a theory of how organisms acquire concepts, associative structures, response biases, and even propositional knowledge. It is commonly acknowledged that associationism took hold after the publishing of John Locke’s Essay Concerning Human Understanding  (1690/1975).[3] However, Locke’s comments on associationism were terse (though fertile), and did not address learning to any great degree. The first serious attempt to detail associationism as a theory of learning was given by Hume in the Treatise of Human Nature  (1738/1975).[4] Hume’s associationism was, first and foremost, a theory connecting how perceptions (“Impressions”) determined trains of thought (successions of “Ideas”). Hume’s empiricism, as enshrined in the Copy  Principle,[5] demanded that there were no Ideas in the mind that were not first given in experience. For Hume, the principles of association constrained the functional role of Ideas once they were copied from Impressions: if Impressions IM1 and IM2 were associated in perception, then their corresponding Ideas, ID1 and ID2 would also become associated. In other words, the ordering of Ideas was determined by the ordering of the Impressions that caused the Ideas to arise.