Gottfried Leibniz

"The principle premisses of Leibniz's philosophy appear to me to be five... : I. Every proposition has a subject and a predicate. II. A subject may have predicates which are qualities existing at various times. (Such a subject is called a substance.) III. True propositions not asserting existence at particular times are necessary and analytic, but such as assert existence at particular times are contingent and synthetic. The latter depend upon final causes. IV. The Ego is a substance. V. Perception yields knowledge of an external world, ie. of existents other than myself and my states. The fundamental objection to Leibniz's philosophy will be found to be the inconsistency of the first premiss with the fourth and fifth; and in this inconsistency we shall find a general objection to Monadism."

"[We] will discuss Soul and Body, the doctrine of God, and Ethics. ...We shall find that Leibniz no longer shows great originality, but tends, with slight alterations of phraseology, to adopt (without acknowledgment) the views of the decried Spinoza. We shall find also many more minor inconsistencies than in the earlier part of [Leibniz's] system, these being due chiefly to the desire to avoid the impieties of the Jewish Atheist, and the still greater impieties to which Leibniz's own logic should have led him."

"Plato, in the Theaetetus, had set to work to refute the identification of knowledge with perception, and from his time onwards almost all philosophers, down to and including Descartes and Leibniz, had taught that much of our most valuable knowledge is not derived from experience."

"In Locke's own day, his chief philosophical opponents were the Cartesians and Leibniz. ...Until the publication of Kant's Critique of Pure Reason in 1781, it might have seemed as if the older philosophical tradition of Descartes, Spinoza, and Leibniz were being definitely overcome by the newer empirical method. The newer method, however, had never prevailed in German universities, and after 1792 it was held responsible for the horrors of the Revolution."

"In Leibniz, a vast edifice of deduction is pyramided upon a pin-point of logical principle. In Leibniz, if the principle is completely true and the deductions are entirely valid, all is well; but the structure in unstable, and the slightest flaw anywhere brings it down in ruins."

"Long before most of these facts were discovered, Leibnitz had conjectured that originally the earth in general, even in the north, enjoyed a much warmer temperature than in the present period of all-ruling and progressive frost; and Buffon and others have established on this idea their hypothesis of a vast central fire in the interior of the earth. The interior parts of the earth and its internal depths are a region totally impervious to the eye of mortal man, and can least of all be approached by those ordinary paths of hypothesis adopted by naturalists and geologists."

"Leibniz's apparent corelessness stands for a fundamental philosophical problem, a quandary that reaches to the foundations of his system of philosophy. In the metaphysics he... presented to the world, Leibniz claimed that the one thing of which we can all be certain is the unity, permanence, immateriality, and absolute immunity to outside influence of the individual mind. In identifying the mind as a "monad"—the Greek word for "unity"—he positioned himself in direct opposition to Spinoza, whose allegedly materialist philosophy of mind he adamantly rejected. And yet the philosopher who made the unity of the individual the fundamental principle of the universe was himself incomparably fragmented, multiplicitous, exposed to the influence of others, and impossible to pin down. How could a monad be so multifarious, not to say nefarious?"

"Leibniz's work lacked the depth and virtuosity of Newton's, but then Leibniz was a librarian, a philosopher, and a diplomat with only a part-time interest in mathematics."

"The lack of early practice in mathematics left its mark on Leibniz's later mathematical style, in which good ideas are sometimes inefficiently developed through lack of technical skill. Often he seemed to lack not only the technique but also the patience to develop the ideas conceived by his wide-ranging imagination."

"Leibnitz, though not propounding any full doctrine on evolution, gave it an impulse by suggesting a view contrary to the sacrosanct belief in the immutability of species... His punishment at the hands of the Church came a few years later, when in 1712, the Jesuits defeated his attempt to found an Academy of Science at Vienna."

"Leibnitz, dominated by ideas of communication, is, in more than one way, the intellectual ancestor of the ideas of this book, for he was also interested in machine computation and in automata. My views in this book are very far from being Leibnitzian, but the problems with which I am concerned are most certainly Leibnitzian. Leibnitz's computing machines were only an offshoot of his interest in a computing language, a reasoning calculus which again was in his mind, merely an extention of his idea of a complete artificial language. Thus, even in his computing machine, Leibnitz's preoccupations were mostly linguistic and communicational."