To support this thesis, O'Grady develops a well-articulated, single level, categorial-type grammar that he uses to analyze syntactic categories, extraction, anaphora, extraposition, and quantifier placement in English and other languages. He shows that such grammars can be constructed via general learning strategies from notions such as dependency, adjacency, precedence, and continuity, and that the available acquisition data points to the emergence of the principles he proposes.

While exploratory, this book provides one of the few serious attempts to develop a theory of grammar and learning that does not posit faculty-specific innate principles. Principles of Grammar and Learning is an exemplary attempt to bring together issues and data from syntactic theory, language acquisition, and the more general study of the human mind.