 One notable feature of this development lies in the fact that Bain was one of the principal exponents and defenders of “associationism”, whose origins, arguably, are to be found most clearly in Hume's Treatise. Associationism is the application of empirical observation to the relation between ideas and experiences. What it seeks is observed regularities, in the hope of formulating psychological laws that will enable us to order the contents of mind. Two such principles—Contiguity and Similarity—were widely accepted, and identified by Bain as being employed by Reid and Hamilton. A third—Contrast—was more disputable, and in “Associationist Controversies” Bain is principally concerned with the nature and identifiable independence of principles such as these.