In pursuit of knowledge.

This article is based on the proposition that to understand the nature of knowledge, and how best to acquire it, one must look first at how the brain abstracts knowledge from the information provided by sensory receptors. The nature of this biological process of knowledge acquisition is suggested by the necessary conditions for the occurrence of learning, and from consideration of these necessary conditions in terms of what is currently known about the properties and limitations of neural systems. This entails discussion of an important distinction that must be made between "perceptual" and "associative" learning and between the neural systems required to mediate these two kinds of learning. There is also discussion of the manner in which language can overcome the limitations of neurological systems to greatly extend the scope of associative learning. This leads on to discussion of the role of active efferent language systems and temporary memory in the mediation of thinking. Consideration of the main features of the biological process of knowledge acquisition confirms, and extends to perception, Hume's famous conclusion that knowledge derives from the similarity or temporal contiguity of recurring events. New insights are also obtained concerning the biological causes of bias in the knowledge acquisition process, concerning the intellectual process of theory generation, and concerning the role of theory in the conduct of empirical research. Finally, and most importantly, it can be concluded that all knowledge is theory and hence that the ultimate goal of science is the development of better theories.