Written by one of today's most creative and innovative philosophers, Ruth Garrett Millikan, this book examines basic empirical concepts; how they are acquired, how they function, and how they have been misrepresented in the traditional philosophical literature. In a radical departure from current philosophical and psychological theories of concepts, this book provides the first in-depth discussion on the psychological act of reidentification. It will be of interest to a broad range of students of philosophy, especially those interested in the application of evolutionary theory to analytic philosophy.