No better sentences could be found with which to conclude this analysis of Leibniz. They resound not only with the grandeur and wide scope characteristic of his thought, but they contain his essential idea, his pre-eminent "note,"--that of the harmony of the natural and the supernatural, the mechanical and the organic. The mechanical is to Leibniz what the word signifies; it is the _instrumental_, and this in the full meaning of the term. Nature is instrumental in that it performs a function, realizes a purpose, and instrumental in the sense that without it spirit, the organic, is an empty dream. The spiritual, on the other hand, is the meaning, the _idea_ of nature. It perfects it, in that it makes it instrumental to itself, and thus renders it not the passive panorama of _mere_ material force, but the manifestation of living spirit. CHAPTER XII. CRITICISM AND CONCLUSION. In the exposition now completed we have in general taken for granted the truth and coherency of Leibniz's fundamental ideas, and have contented ourselves with an account of the principles and notions that flow from these ideas. The time has come for retracing our steps, and for inquiring whether the assumed premises can be thus unquestioningly adopted. This final chapter, therefore, we shall devote to criticism of the basis of Leibniz's philosophy, not attempting to test it by a comparison with other systems, but by inquiring into its internal coherency, and by a brief account of the ways in which his successors, or at least one of them, endeavored to make right the points in which he appeared to fail. The fundamental contradiction in Leibniz is to be found, I believe, between the method which he adopted--without inquiry into its validity and scope--and the subject-matter, or perhaps better the attitude, to which he attempted to apply this method; between, that is to say, the scholastic formal logic on the one hand and the idea of inter-relation derived from the development of scientific thought, on the other. Leibniz never thought of investigating the formal logic bequeathed by scholasticism, with a view to determining its adequacy as philosophic method. He adopted, as we have seen, the principles of identity and contradiction as sole principles of the only perfect knowledge. The type of knowledge is that which can be reduced to a series of identical propositions, whose opposite is seen to be impossible, because self-contradictory. Only knowledge in this form can be said to be demonstrative and necessary. As against Locke he justified the syllogistic method of the schoolmen as the typical method of all rational truth.