INTRODUCTION
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To see how Leibniz fits with other modern philosophers chronologically, look at the datechart (return by clicking BACK on the Netscape toolbar). You might also look at the map of philosophers’ places of birth, which shows how the philosophical centre of gravity gradually moved northwards (with the notable exceptions of Bacon and Hobbes).
Go to a short biography of Leibniz.
As you have learned, Leibniz’s life as a philosopher was unusual in that it was not punctuated by the publication of major philosophical works. Indeed, his public life can be described virtually without reference to his philosophy, which was conducted mostly through correspondence and journal articles.
Go to a brief description of Leibniz’s writings.
I have not provided a summary of Leibniz’s philosophy, since you are about to read the last of Leibniz’s own summaries, namely the Monadology. This way you get it from the horse’s mouth, even if it is more difficult to understand than a summary written by a third party three centuries later. If you want to know what I would have said, you can always read my little Past Masters: Leibniz (Oxford, 1984).
Nevertheless, a few words of background might help.
On the whole, Germany was slower to pick up the new ideas of the Renaissance and the early modern movement than Italy, France, and England. Leibniz had an intense but generally rather conservative education in the classics, science, philosophy, and law. His first and enduring experience of philosophy was through scholastic Aristotelianism, and, unlike virtually all the other modern philosophers, he never lost his respect for Aristotle, and later scholastics such as Suárez. For example, he insisted that every substance has a substantial form as well as matter, and that everything has a final as well as an efficient cause. He also accepted the broad validity of Aristotelian logic, and tried to reform it instead of abandoning it like other modern philosophers. His attempt to mathematise logic came very close to the symbolic logic developed in the 20th century, and it remained largely unrecognised until rediscovered by Russell and Couturat.
Leibniz himself reports that, when an impressionable young university student, he went through a period in which he was converted to materialism. He read Hobbes avidly, and wrote him a couple of lengthy fan letters in 1670, when Hobbes was 82 (and still fully compos). However, there is no record of Hobbes having replied, or even having received the letters. Although Leibniz’s philosophy developed away from materialism, it left strong traces in his mature system: for example, the belief that every event has a mechanical explanation, and that a soul can never be without a body. He also retained some ideas specific to Hobbes, such as the theory of appetition or conation, which was an infinitesimal beginning of motion; and the reduction of logic to the addition and subtraction of concepts.
The influence of Descartes, and Cartesians such as Arnauld and Malebranche, is more difficult to assess. In many ways they had set the agenda for philosophical debate in the second half of the 17th century. Particularly as a result of his lengthy stay in Paris and his research on unpublished Descartes manuscripts, Leibniz inevitably absorbed a lot of Cartesian concepts and terminology. He shared the modern belief in a mechanical, material universe; but Leibniz’s philosophical system was more a criticism of, and reaction against Cartesianism, than an offshoot of it. In particular, he rejected the concept of immaterial substance (apart from God), and of any interaction between mind and matter. Importantly also, he rejected the idea that extension was a single substance, and held instead that it was a compound of infinitely many simple substances.
The influence of Spinoza is also difficult to assess. Although he read the Ethics and had 4 days of discussion with Spinoza in 1676, he was already 30, and the main ingredients of his mature system were already in place. I am sceptical of the claim of some scholars that Spinoza was a major influence, partly because their systems are essentially so different, and partly because a number of things they had in common probably come from Hobbes. Nevertheless, there is some plausibility to the idea that Spinoza’s ‘double-aspect’ theory of the relation between the mind of body at least reinforced Leibniz’s own thinking along those lines.
As for other influences, it must always be borne in mind that a historical perspective tends to put a small number of ‘great’ philosophers on a pedestal, and leave the rest out of account. But the distinction would be nothing like as sharp at the time. For example, as far as Leibniz was concerned, Spinoza was just one philosopher among many, whom he happened to have met. His philosophy was dangerous; he had published hardly anything; and Leibniz was probably more interested in his skills as a lens grinder. At the time, there was a strong fashion for what one might call ‘mystical philosophy’, which drew its inspiration from such sources as neoplatonism, cabalism, natural magic, vitalism, astrology, alchemy, etc. Those who regarded the writings of mystical philosophers as superstitious nonsense were in a small minority at the time. It was not until around 1700 that the mechanistic and materialist Newtonian world-view suddenly became dominant. Leibniz was well read in the mystical literature, and many of its proponents were his personal friends. Its influence clearly shows in many of Leibniz’s writings, and the Monadology is a particularly good example, with its almost mystical vision of universal animism, a form of reincarnation, worlds within worlds, and the special relation between God and humanity. The Monadology would not have seemed nearly as bizarre to Leibniz’s contemporaries is it does to us now.
There is a similar point to be made about the ancient philosophers. Nowadays we tend to think of the ancient world as having thrown up just two great philosophers in its thousand years of continuous history — namely Plato and Aristotle. But, while for the scholastics Aristotle did have a special status, for those who rejected scholasticism (and despite his respect for it, Leibnz did reject it), there was no presumption that only Plato and Aristotle should be taken seriously. Throughout the Renaissance and early modern period, philosophers saw all ancient philosophers as a potential source of knowledge and inspiration. Athough Leibniz took Plato and Aristotle seriously, he also took seriously presocratic philosophers such as Pythagoras and Hericlitus, and later philosophers such as the Stoics and the neoplatonists. He was influenced by the Renaissance humanist idea that most of the major insights into the nature of reality had already been obtained by one or other of the ancient philosophers, and he was not ashamed to give credit for his own views to (now unfashionable) thinkers such as Pythagoras.
Finally, we must never lose sight of Leibniz’s own dictum, that philosophers are generally right in what they assert, and wrong in what they deny. It is as if they are all looking at a town on a hill from different points of view. They all have some of the truth, and they only go wrong in failing to recognise the limitations of their own perspective, and in denying the truth of what others see. Leibniz’s ultimate ambition was to reconcile all these differences by adopting a God-like perspective, in which all the different points of view came together into a single, harmonious whole. In short, Leibniz himself made a virtue of eclecticism, and accepted a wide range of influences. If he was right, we shouldn’t bother ourselves with questions like whether he was really a Spinozist, or really a renegade Cartesian, or really a neo-Aristotelian, or really a neo-Platonist. He was all of these, and none.