Brain and Cognition 42, 44–46 (2000) doi:10.1006/brcg.1999.1157, available online at http://www.idealibrary.com on What Matters in the Third Millenium Paul Eling NICI, University of Nijmegen Looking Back Before Descartes, body and mind were integrated. Descartes introduced the notion of two independent entities, thereby creating a problem rather than solving one. Disregarding the validity question, the dualistic approach may seem handy: one can concentrate on either neuro-anatomy/neurophysiology or behavior, without bothering too much about the relation between these two aspects (but a monist would not understand that, of course). A relative distance between brain theories and behavior theories characterizes the post- Cartesian era. In the past few decades we witnessed an approach of brain and behavior again, putting an end to the Cartesian period. Looking Forward The new era will be characterized by the study of behavior in terms of matter. For Descartes, ‘‘matter’’ implied the conception of the body as a machine. Hardly anything was known about (organic) chemistry. Now, we think of the mind in terms of neurochemistry. This new look at the material basis of behavior will have implications for the type of models, the questions, and the methodology used by neuroscientists. Some of the consequences of this new approach will be mentioned below. There has been no new La Mettrie to preach the dogma of materialism. Yet, the new approach dispersed in the literature in an almost imperceptible way, in accordance with the rules for reporting one’s research: not too much ‘‘space’’ was spent on the philosophical background. Most (cognitive) neu- roscientists do not bother to explicate their metaphysical positions. But it is obvious that they are materialists, whether they are acquainted with the chemical materials or not. Address correspondence and reprint requests to Paul Eling, NICI, University of Nijmegen, P.O. Box 9104, 6500 HE Nijmegen, The Netherlands. E-mail: eling@nici.kun.nl. 44 0278-2626/00 $35.00 Copyright  2000 by Academic Press All rights of reproduction in any form reserved.