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420 intended to treat of all these in detail, but in no case was that intention carried out, though we know from the closing sections of the Principles the general lines on which he would have handled the problems of mathematics and physics. And we have several tracts dealing with these sciences, e.g., Arithmetica, Miscellanea Mathematica, De Motu, The Analyst, and A Defence of Free Thinking in Mathematics. It was Berkeley's purpose to deal with ethics in Part II of the Principles. He set to work on this undertaking after Part I (what we know as the Principles) was completed, but never finished it. The unfinished manuscript was lost during his travels in Italy and he never attempted to re-write it.

But though accident has deprived us of this specifically ethical treatise, yet scattered up and down Berkeley's work there is a fair amount of writing on ethical subjects. It is enough not merely to enable us to reconstruct the main outlines of Berkeley's system, but also to trace the development of his views. The Commonplace Book teems with suggestive remarks, which probably give some idea of the argument of the lost Part II of the Principles. In addition, three of the dialogues in Alciphron are mainly ethical, and there is much valuable matter in Passive Obedience.

Berkeley's jottings in the Commonplace Book show that in ethics, as in other departments of philosophy, he was deeply influenced by Locke. Such isolated entries as "Morality may be demonstrated as mixt Mathematics," cannot be understood without reference to Locke. Most of Berkeley's memoranda in the Commonplace Book have Locke in view; and in order to appreciate their meaning it is necessary to have in mind Locke's theory of ethics. Ethics, for Locke, is a perfectly demonstrable science, because