John Locke is one of the great figures of the modern philosophical pantheon. No study of the history of thought since the seventeenth century can ignore him. In the close confines of university philosophy departments his Essay Concerning Human Understanding is read (in parts), or read about, by students instructed to examine his criticism of the doctrine of innate ideas, or his theory of perception and the correlative distinction between primary and secondary qualities, or his famous discussion of the problem of personal identity. 

But in the real world Locke’s writings have been even more significant. His Two Treatises of Government was quoted extensively and verbatim in the documents of the American and French revolutions, and they, together with the Essay and his writings on religious toleration, made him one of the two heroes