This collection of essays serves both as an introduction to Ruth Millikan's much-discussed volume Language, Thought, and Other Biological Categories and as an extension and application of Millikan's central themes, especially in the philosophy of psychology.

The title essay discusses meaning rationalism and argues that rationality is not in the head, indeed, that there is no legitimate interpretation under which logical possibility and necessity are known a priori. In other essays, Millikan clarifies her views on the nature of mental representation, explores whether human thought is a product of natural selection, examines the nature of behavior as studied by the behavioral sciences, and discusses the issues of individualism in psychology, psychological explanation, indexicality in thought, what knowledge is, and the realism/antirealism debate.