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The Rationalism of Descartes and Leibniz
Although philosophy rarely alters its direction and mood with sudden swings, there are times when its new concerns and emphases clearly separate it from its immediate past. Such was the case with seventeenth-century Continental rationalism, whose founder was Rene Descartes and whose new program initiated what is called modern philosophy. In a sense, much of what the Continental rationalists set out to do had already been attempted by the medieval philosophers and by Bacon and Hobbes. But Descartes and Leibniz fashioned a new ideal for philosophy. Influenced by the progress and success of science and mathematics, their new program was an attempt to provide philosophy with the exactness of mathematics. They set out to formulate clear and rational principles that could be organized into a system of truths from which accurate information about the world could be deduced. Their emphasis was upon the rational ability of the human mind, which they now considered the source of truth both about man and about the world. Even though they did not reject the claims of religion, they did consider philosophical reasoning something different than supernatural revelation. They saw little value in feeling and enthusiasm as means for discovering truth, but they did believe that the mind of an individual is structured in such a way that simply by operating according to the appropriate method it can discover the nature of the universe. The rationalists assumed that what they could think clearly with their minds did in fact exist in the world outside their minds. Descartes and Leibniz even argued that certain ideas are innate in the human mind, that, given the proper occasion, experience would cause these innate truths to become self-evident. That the highly optimistic program of rationalism was not altogether successful is indicated in the differences of the systems it produced. These two rationalists finally interpreted the natural world after the mechanical model of physics and believed that determinism was the cause of all physical events. Descartes described reality as a dualism consisting of two basic elements, thought and extension, whereas Leibniz, a pluralist, said that although there is only one kind of substance, the monad, there are nevertheless different kinds of monads accounting for the various elements in nature. In this paper, I will provide a general overview of these two rationalist attempts at creating a formula for truth and raise some of the more common empirical problems that apply to each.
Being a mathematician, Descartes believed that a method was necessary to give his thoughts some structure and a path that could apply to all deductions of truth. In a need for a method, Descartes hypothesized that all men have virtually the same genetic disposition to reason and that the differences in opinion and error in reasoning are due to how that reason is applied. Thus he contends that there is a need for social norms of reason that emulate the certainty of mathematics. “My method,” he writes, “contains everything which gives certainty to the rules of arithmetic.” In it he says that we should never accept anything except clear and distinct ideas, divide each problem into as many parts as are needed to solve it, and always check thoroughly for oversights. If knowledge is to be found without error, he said that it must be by using the principles of clarity and distinctness. In this way he said that knowledge would be indubitable.
To lay the groundwork for this method, Descartes establishes the idea of belief by doubting. He doubts anything that is not self-evident by intuition. A casualty of this doubt is all of his empirical belief. To this end he gives two examples as to why he can’t believe the conclusions drawn using his own senses.
The first of these is the dream argument. The basic layout of the argument for dreaming is that if it’s possible that we are dreaming, we cannot have empirical beliefs. It is possible that we are dreaming, so we can’t have certain knowledge regarding empirical beliefs. To further illustrate his skepticism regarding empirical beliefs, he proposes the purely theoretical “evil demon” argument. In it he argues that if it is possible that we are deceived by an evil god, then we cant know anything with certainty. Since it is possible that we are being deceived by an evil god, then we cannot know with certainty. These arguments were made to establish that it is possible that either through perceptual error or cognitive dysfunction, we may be deceived and not know with certainty.
In light of his newfound credo of doubt and skepticism, he finds himself questioning his very existence. If in fact it is possible that an evil god is tricking him, could it also be possible that he doesn’t really exist at all? To prove his existence he uses the maxim of “Cogito ergo sum”, or “I think therefore I am”. The only thing that could not be doubted is that he thought something, even if it was thinking he was dreaming or being tricked, or thinking that he didn’t have a body. This was what he saw as the first true principle and the basis for any further inquiry. This led him to suppose that the essence of being was thinking, and furthermore, that the mind was separate from the body.
This was a foundation, but it had one problem. It only proved that he existed. He had no way to show that his surroundings, including other people, existed. Descartes realized for this and other reasons that he needed to prove God’s existence. God could be the only guarantee that our clear and distinct ideas are true, and that we are not being tricked by an evil demon.
For this, Descartes was happy enough to use a version of Anselm’s ontological proof to argue that the idea of a perfect God must have a cause. Since we are a pretty hopeless when it comes to perfection, it couldn’t be us, so God must be the cause of our idea of his perfection. He writes that, ” the more perfect…cannot be a consequence of…the less perfect.” The very idea of perfection implies existence, so to speak of a non-existent perfection is to engage in contradiction. For Descartes, God seems to fall into the realm of a Platonic form of God, an apriori existence. From his own existence, Descartes “proved” God’s existence and it was also in this way that Descartes proved that his external world existed.
This brings us back to the mind-body problem. Having said the mind and the body were separate, Descartes then had to explain how they worked together in seemingly perfect unison. His theory began with one absolute substance, God, and two relative substances, mind and matter. Man, then, partakes of the two relative substances of which all else in the universe is made. Man is of the universe, for Descartes. As part of nature, he is mechanical to the extreme; he is a machine which operates by natural laws just as a watch might operate. These determinist ideas were to have a long influence and were propagated along with a similar dualism in the philosophy of Leibniz.
Leibniz was probably the supreme intellect of his age, writing on many subjects, as well as inventing the differential calculus. Most of what he published while alive was similar to Descartes in its content in that it was limited to what the Royalty and those in charge wanted to believe. In public Leibniz propounded the “principle of the best”, which among other things, argued that God has created the best possible world.
Leibniz believed that finite substances, things like you and I, are composed of simples. He called these simples monads. The word monad comes from the Greek for unity which reflects the harmony he saw in the monad. He used an argument based on composition to argue for monads. He said that a substance is either a composite or a simple. If it’s a composite it can be divided, and if it can be divided, the division cannot continue infinitely. Division must end with an indivisible substance. Therefore, there are simple indivisible things. These are things that Leibniz has named monads. He says that these monads are non-extended, non-material, and by nature they are immortal.
Leibniz’s philosophy sees people as only partly distinct from everything else that exists. Everything, people included, is made up of monads. All monads have similar properties, but each monad is different. No two monads are exactly alike, but they function in complete harmony. He compares them to “several different bands of musicians or choirs, playing their parts separately, and so placed that they do not see or even hear one another…nevertheless [they] keep perfect together, by each following their own notes, in such a way that he who hears them all finds in them a harmony that is wonderful, and much more surprising than if there had been any connection between them.” Different monads have greater or less ability to see what’s going on around them. Those monads with the most ability to think and perceive are human souls. All monads, reflect the world, they are “windowless”.
In his philosophy, each monad seems to be like a point of view for seeing everything, and everything is actually made up of an infinite number of different points of view. Leibniz believed that the world has infinite variety. At the same time, everything is connected, not only in fact, but logically too, in that it all makes sense together. Leibniz said that if people (or monads) had infinite minds like God, we would be able to understand everything in its infinite variety just by looking at one individual thing. Nevertheless, we don’t have infinite minds and can only understand certain things about the world. Only God can see the big picture. This means that things that may seem accidental to us are still part of God’s plan.
This way of looking at things means that there is no real difference between innate and acquired characteristics. What happens to you is just as much a part of you as what you already are. The difference is in how people see things. Different things might happen to you in another possible world, but that world would not be as good as this one. Leibniz said that God chose to make the world be the way it is because this world is “the best of all possible worlds.” According to Leibniz, a better world could not possibly have existed. Leibniz’s ideas about what makes for the best possible world are based on mathematical ideas. As a mathematician, Leibniz looked for the simplest explanations that would account for the greatest number of numerical relationships. And as a philosopher, he believed God set up the world so that the simplest reasons would account for the most variety.
Like Descartes, Leibniz didn’t leave much room in his world for free will. Leibniz believed that everything that happens is a result of what already exists. In turn, what exists depends on God. Because God might have caused things to be different, there is a certain amount of free play in Leibniz’s system. The facts might have been different, but logically it must make the best sense for them to be the way they are.
The dualism of their rationalist philosophies made a neat separation between physical and metaphysical reality. An important result of this separation was that it allowed philosophers and scientists to study the natural world without having to worry about supernatural questions. In fact since their time, many philosophers have argued that we should stop asking metaphysical questions. While the contributions of Descartes and Leibnitz created a new path for the philosophers to come, their philosophies have not escaped the criticisms and arguments of others.
The empiricists main complaint was that the rationalists had no hard evidence for their theories. One opposing view which was held by Hume is that no investigation could reveal an immaterial, indivisible, imperishable soul-substance. He writes, “When I enter intimately upon what I call myself, I always stumble on some particular perception of pain or pleasure. I never catch myself, at any time, without a perception, and never can observe anything but the perception.” The rationalists seemed to have no problem with an illogical leap of faith. It was needed to continue the journey. Since the philosophies of Descartes and Leibniz were built around this idea of an immaterial, indivisible God, the philosophy that followed seemed to many to be shaky and speculative by their own definition. But considering the time period and the pressure involved in philosophizing at all, we must admire and respect the great advancement in thinking that was prompted by these great men.
Mates, B. The Philosophy of Leibniz. New York and Oxford: Oxford University Press, 1986.
Descartes, Rene. The Philosophical Writings, tr. John Cottingham and Dugald Murdoch. Cambridge: Cambridge University Press, 1985.
Bricke, John. Hume’s Philosophy of Mind. Princeton: Princeton University Press, 1980.
Matson, Wallace. A New History of Philosophy. Harcourt Brace Jovanovich, Inc., 1987.
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