Thomas Brown (1778-1820) of the Scottish School puts the finishing touches to associationism: His laws of suggestion (i.e. association) were resemblance, contrast, and nearness in space and time, just like Aristotle's. He added a set of secondary laws -- duration, liveliness, frequency, and recency -- that strengthened suggestions. Then he considered as well the degrees of coexistence with other associations, constitutional differences of mind or temperament, differing circumstances of the moment, state of health or efficiency of the body, and prior habits. Finally, he understood association as an active process of an active, holistic mind.

Alexander Bain (1818-1903), a lifelong friend of John Stuart Mill, connected associationism with physiology. Accepting the law of contiguity, similarity, and frequency, he viewed them, as had Hartley, as neurological. He added the law of compound association, which says that most associations are among whole clusters of other associations. And he added the law of constructive association, which says that we can also actively, creatively, add to our associations ourselves.

One of Bain's basic principles is immortalized as the Spencer-Bain principle: The frequency or probability of a behavior rises if it is followed by a pleasurable event, and decreases if it is followed by a painful event. This is, of course, the same principle that the behaviorists would elaborate on a century later.

Bain has an even larger role in the history of psychology. First, he is often given the credit of having written two of the earliest textbooks in psychology -- The Senses and the Intellect (1855) and Emotions and the Will (1859), both of which went through many editions, and were used, for example, by William James. He also founded the first English-language psychological journal, called Mind, in January of 1876.