Paul Thompson's new book,The Structure of Biological Theories, is about the formalization of evolutionary biology. He is primarily concerned, he says, with the logical, epistemological, and methodological aspects of biological theorizing. The main theme of the book is the opposition between what Thompson calls the syntactic and the semantic conceptions of theories. He wishes to establish that the semantic account is superior to the syntactic in at least three areas: first, it offers a more faithful account of population biology; second, it facilitates a conception of evolutionary biology as a family of interacting theories; finally, it offers us a richer framework for the resolution of methodological problems that have plagued sociobiology and evolutionary epistemology.