Berkeley takes Locke as the representative advocate of the "abstract ideas" against which he wages war in the Introduction to the _Principles_. Under cover of an ambiguity in the term _idea_, he is unconsciously fighting against a man of straw. He supposes that Locke means by _idea_ only a concrete datum of sense, or of imagination; and he argues that we cannot without contradiction abstract from all such data, and yet retain idea. But Locke includes among _his_ ideas intellectual relations--what Berkeley himself afterwards distinguished as _notions_, in contrast with ideas. This polemic against Locke is therefore one of verbal confusion. In later life he probably saw this, as he saw deeper into the whole question involved. This is suggested by the omission of the argument against abstract ideas, given in earlier editions of _Alciphron_, from the edition published a year before he died. In his juvenile attack on abstractions, his characteristic impetuosity seems to carry him to the extreme of rejecting rational relations that are involved in the objectivity of sensible things and natural order, thus resting experience at last only on phenomena--particular and contingent.
A preparatory draft of the Introduction to the _Principles_, which I found in the manuscript department of the library of Trinity College, Dublin, is printed in the appendix to this edition of Berkeley's Philosophical Works. The variations are of some interest, biographical and philosophical. It seems to have been written in the autumn of 1708, and it may with advantage be compared with the text of the finished Introduction, as well as with numerous relative entries in the _Commonplace Book_.
After this Introduction, the New Principles themselves are evolved, in a corresponding spirit of hostility to empty abstractions. The sections may be thus divided:--
i. Rationale of the Principles (sect. 1-33).
ii. Supposed Objections to the Principles answered (sect. 34-84).
iii. Consequences and Applications of the Principles (sect. 85-156).
The reader may remember that one of the entries in the _Commonplace Book_ runs as follows:--"To begin the First Book, not with mention of sensation and reflexion, but, instead of sensation, to use perception, or thought in general." Berkeley seems there to be oscillating between Locke and Descartes. He now adopts Locke's account of the materials of which our concrete experience consists (sect. 1). The data of human knowledge of existence are accordingly found in the ideas, phenomena, or appearances (_a_) of which we are percipient in the senses, and (_b_) of which we are conscious when we attend to our inward passions and operations--all which make up the original contents of human experience, to be reproduced in new forms and arrangements, (_c_) in memory and (_d_) imagination and (_e_) expectation. Those materials are called _ideas_ because living mind or spirit is the indispensable realising factor: they all presuppose living mind, spirit, self, or ego to realise and elaborate them (sect. 2). This is implied in our use of personal pronouns, which signify, not ideas of any of the preceding kinds, but that which is "entirely distinct from them, wherein they exist, or, which is the same thing, by which they are perceived." In this fundamental presupposition Descartes is more apparent than Locke, and there is even an unconscious forecast of Kant and Hegel.