Although this book was brewing for a number of years, it owes many aspects of its present form to a series of discussions with Richard Francis during 1992 and 1993. Through these discussions a vague plan to investigate the “function of mind in nature,” and the relations between intelligence and environmental complexity, took on a more definite shape. It was also in these discussions that this set of questions in the philosophy of mind became linked to more general issues about the relations between organisms and environments, and the general pattern of “externalist” explanations – explanations of internal properties of organic systems in terms of external properties.

So the book is intended to address two types of questions at once. First, is it possible to develop an informative philosophical theory about the mind, by linking mind to properties of environmental complexity? The second set of questions concerns externalist patterns of explanation in general. What are these explanations like? What are the characteristic debates and issues that surround the attempt to understand the internal in terms of the external?

I see these questions as closely linked, and in this book they are often examined simultaneously. However, for practical reasons the book is divided into two parts which are largely self-contained. This division is partly methodological and partly a matter of content. Part I is intended as a self-contained essay in the philosophy of mind, and it is completely nontechnical.