Published in 1890, William James’ manual, The principles of psychology, followed by Psychology (lectures) in 1892, form the foundation of behaviorism. The same year, Animal life and intelligence by C. Lloyd Morgan correlates with James’ view, extending it to wildlife. The next step was taken by Lloyd Morgan, with the publication of An introduction to comparative psychology (1894), in which the issue of trial and error learning in animals receives a systematic approach, thus pointing research to a specific area and interpretive apparatus that will ultimately lead to the full crystallization of behaviorism’s ideas in the past century. The most prestigious version of behaviorism, that of psychological behaviorism, has strong historical roots; in this way, one can invoke the works of Aristotle (On Nature). Another version of behaviorism, like that suggested by Gilbert Ryle, is logical behaviorism. Long before that, however, classical British empiricists, led by John Locke (1632-1704) and David Hume (1711-1776), used associationist prescriptions to reveal cause-effect coupling in mental phenomena.