There is internal evidence in the book of _Principles_ that its author had been a diligent and critical student of Locke’s _Essay_. Like the _Essay_, it is dedicated to the Earl of Pembroke. The word _idea_ is not less characteristic of the _Principles_ than of the _Essay_, although Berkeley generally uses it with a narrower application than Locke, confining it to phenomena presented objectively to our senses, and their subjective reproductions in imagination. With both Berkeley and Locke objective phenomena (under the name of ideas) are the materials supplied to man for conversion into natural science. Locke’s reduction of ideas into simple and complex, as well as some of his subdivisions, reappear with modifications in the _Principles_. Berkeley’s account of Substance and Power, Space and Time, while different from Locke’s, still bears marks of the _Essay_. Concrete Substance, which in its ultimate meaning much perplexes Locke, is identified with the personal pronouns “I” and “you” by Berkeley, and is thus spiritualised. Cause proper, or Power, he finds only in the voluntary activity of persons. Space is presented to us in our sensuous experience of resistance to organic movements; while it is symbolised in terms of phenomena presented to sight, as already explained in the _Essay on Vision_. Time is revealed in our actual experience of change in the ideas or phenomena of which we are percipient in sense; length of time being calculated by the changes in the adopted measure of duration. Infinite space and infinite time, being necessarily incapable of finite ideation, are dismissed as abstractions that for man must always be empty of realisable meaning. Indeed, the _Commonplace Book_ shews that Locke influenced Berkeley as much by antagonism as otherwise. “Such was the candour of that great man that I persuade myself, were he alive, he would not be offended that I differed from him, seeing that in so doing I follow his advice to use my own judgment, see with my own eyes and not with another’s.” So he argues against Locke’s opinions about the infinity and eternity of space, and the possibility of matter endowed with power to think, and urges his inconsistency in treating some qualities of matter as wholly material, while he insists that others, under the name of “secondary,” are necessarily dependent on sentient intelligence. Above all he assails Locke’s “abstract ideas” as germs of scepticism—interpreting Locke’s meaning paradoxically.