Locke's chief work, _An Essay concerning Human Understanding_, which had been planned as early as 1670, was published in 1689-90, a short abstract of it having previously appeared in French in Le Clerc's _Bibliothèque Universelle_, 1688. His theoretical works include, further, the two posthumous treatises, _On the Conduct of the Understanding_ (originally intended for incorporation in the fourth edition of the _Essay_, which, however, appeared in 1700 without this chapter, which probably had proved too extended) and the _Elements of Natural Philosophy_. To political and politico-economic questions Locke contributed the two _Treatises on Government_, 1690, and three essays on money and the coinage. In the year 1689 appeared the first of three _Letters on Tolerance_, followed, in 1693, by _Some Thoughts on Education_, and, in 1695, by _The Reasonableness of Christianity as delivered in the Scriptures_. The collected works appeared for the first time in 1714, and in nine volumes in 1853; the philosophical works (edited by St. John) are given in Bonn's Standard Library (1867-68).[1] [Footnote 1: Lord King and Fox Bourne have written on Locke's life, 1829 and 1876. A comparison of Locke's theory of knowledge with Leibnitz's critique was published by Hartenstein in 1865, and one by Von Benoit (prize dissertation) in 1869, and an exposition of his theory of substance by De Fries in 1879. Victor Cousin's _Philosophie de Locke_ has passed through six editions. [Among more recent English discussions reference may be made to Green's Introduction to Hume's _Treatise on Human Nature_, 1874 (new ed. 1890), which is a valuable critique of the line of development, Locke, Berkeley, Hume; Fowler's _Locke_, in the English Men of Letters, 1880; and Fraser's _Locke_, in Blackwood's Philosophical Classics, 1890.--TR.]]