New in paperback. Hardcover was published in 2014. This interdiciplinary book considers the relationship between language and thought from a philosphical perspective, drawing both on the philosophical study of language and the purely formal study of grammar, and arguing that the two should align. The claim is that grammer provides homo sapiens with the ability to think in certain grammatical ways and that this in turn explains the vast cognitive powers of human beings. Evidence is considered from biology, the evolution of language, language disorders, and linguistic phenomena.