Ruth Millikan's extended argument for a biological view of the study of cognition in Language, Thought, and Other Biological Categories caught the attention of the philosophical community. Universally regarded as an important, even brilliant, work, its complexity and dense presentation made it difficult to plumb. This collection of essays serves both as an introduction to that much discussed volume and as an extension and application of Millikan's central and controversial themes, especially in the philosophy of psychology. The title essay, referring to the White Queen's practice of exercising her mind by believing impossible things, 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. Nor are there any laws of rational psychology. Rationality is not a lawful occurrence but a biological norm that is effected in an integrated head-world system under biologically ideal conditions. 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.