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 proposed to the thinking world an insoluble problem, when he sought to reach the extreme theory of knowledge, self-consciousness alone being given.

Leibnitz saw the insufficiency of the Cartesian principle. He longed to solve the hitherto unsolved difficulty of a First Philosophy. Des Cartes, by directing him to the mind itself, through which we reflect, had, for the first time, clearly shown the quarter in which, those results of which he was in quest are to be found. The maxim of the school of Locke was "nihil est in intellectu nisi quod prius in sensu." The famous addition, "nisi intellectus ipse" expresses the distinctive peculiarity of Leibnitz. But how is the "intellectus ipse" to be distinguished from the "quod prius in sensu?" The discovery of a test for marking this distinction, is an important addition made by him to the common stock of philosophical principle. He has expressed its nature, among other places, in a letter to Bieling, in which, speaking of Locke, he asserts that he has "no idea of the demonstrative metaphysics. Could he have made the distinction between necessary truth, which we obtain by intuition, and those other truths which we reach by experience, he would have found that the senses teach us only what takes place, not what must take place." All those ideas which we are compelled to think, accordingly, belong to the very structure of the soul itself, and are to be included as articles of our original Faith. The critical