Understanding Rationalism
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Understanding Rationalism

Charlie Huenemann

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eBook - ePub

Understanding Rationalism

Charlie Huenemann

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The three great historical philosophers most often associated with rationalism - Descartes, Spinoza and Leibniz - opened up ingenious and breathtaking vistas upon the world. Yet their works are so difficult that readers often find themselves stymied. "Understanding Rationalism" offers a guide for anyone approaching these thinkers for the first time.With clear explanations, elegant examples and insightful summaries, "Understanding Rationalism" unlocks their intricate metaphysical systems, which are by turns surprising, compelling and sometimes bizarre. It also lays out their controversial stances on moral, political and religious problems. The study is framed by an opening discussion of the broad themes and attitudes common to these three philosophers and a closing analysis of the legacy they left for the rest of philosophy.

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Descartes's dualistic world


René Descartes was born in La Haye, France, in 1596. His mother died less than a year later, after giving birth to Descartes’s sister, and soon thereafter his father began travelling away on legal and political business for more than six months out of the year. Descartes and his sister and their older brother were left in the care of friends and relatives, and by the time he was ten, Descartes was sent away to a rigorous Jesuit boarding school aimed at turning boys into pious and gracious gentlemen. He was bookish, small, and weak in health. He received a thorough education in classical literature and Latin, and excelled in mathematics. After boarding school he followed family tradition and studied to be a lawyer, and received his law degree by the time he was 20. But by then he realized that he did not want to be a lawyer, and he was not sure what to do with himself.
It was expected that his older brother would inherit his father’s title and most of his wealth, and Descartes was not entitled to any share in the family’s holdings until he turned 25. So for the next five years Descartes signed up with the military and served in various capacities as a soldier throughout France, Holland and Germany. Not much is known about his activities, although we know that he continued to develop his knowledge of mathematics and physics, and began to form a vision of his own philosophy. He also learned the art of gambling, and – given his skills in mathematics – he was probably pretty good at it.
When he turned 25 he took possession of some family properties and promptly sold them. And again for the next six or seven years little is known about his endeavours. He travelled to Italy, spent most of his time in Paris, made friends, and continued with his studies in mathematics and science – and of course probably did all the things any young man of independent means would do while trying to find his way in the world. He was a disappointment to his father and older brother, who would have preferred Descartes to become serious and establish a more stable and secure mode of life.
By 1628, as he entered his thirties, he was ready to leave the diversions and controversies of Paris and hide himself in rural Holland. He had found his direction. He felt that he had a genuine contribution to make in philosophy, and he needed to be free of distraction in order to make it. It was clear to him that our vision of the world needs to be firmly grounded in the results of science, experiments and mathematics. So he began experimenting, making lenses, practising dissection, and deducing his own conclusions. By 1633 he had bound up his view of the world in a work he aptly entitled The World, and was ready to send it to the publishers, when he received startling news: the Catholic Church had condemned Galileo for his belief that the earth revolved around the sun. Descartes had agreed with Galileo, and had said so in The World. He certainly did not want to be condemned and (like Galileo) placed under house arrest for the rest of his life, and so he was not sure what to do.
He retreated and regrouped, and reworked The World into a set of separate essays on geometry, optics and meteorology, all prefaced with a Discourse on Method, published in 1637. This was followed four years later by a work that laid the metaphysical groundwork for his scientific approach to the world, Meditations on First Philosophy. He published the Meditations with a set of objections from several notable European intellectuals, and his replies to them. This was followed four years later by his four-part Principles of Philosophy, a work that explained the entire Cartesian system and was intended by its author to become the standard textbook for philosophy and natural science throughout Europe. It very nearly did.
Descartes held as his motto that “he who is hidden lives well”, but his publications brought him into the public spotlight. He was recognized immediately as among the top mathematicians of his time, and people saw him as a fiercely intelligent critic of the established scientific, philosophical and theological orthodoxy – an intellectual rebel. Many saw him as he presented himself: a spokesman for plain sense, crashing through the delicate lattice of scholastic philosophy with the battering ram of the new experimental, mechanical science. (Once, when someone asked to see his library, Descartes showed him a body he was dissecting and said, “This is my library.”) And as often as he was attacked, he answered back with matching vehemence and venom – which only inflamed his enemies all the more, of course. He never yielded an inch to his critics and often made it seem as if they simply had not read his works carefully enough. At the very least, his replies to critics are stunning intellectual performances on his part.
We can sense an interesting tension between Descartes’s works and his life. His works suggest a solo act, that of a man who is more interested in conquering himself than the world, and a man who wants nothing but some peace in which to carry out his own reasonable meditations on philosophy, mathematics and nature. But his life was filled with friends, enemies, jealousy, pride, fame and controversy. He was father to a daughter, Francine, whom he cherished, and who was taken from him by sickness when she was just five years old. He never married, nor (from what we know) had romantic attachments after that. His last published work was The Passions of the Soul (1649), in which he tried to teach how to keep one’s health, cheer and tranquillity even when facing the harshest tragedies of life.
He became increasingly entangled in scholarly and religious controversies through the late 1640s, and in 1649 he accepted an invitation to serve as tutor to Christina, the Queen of Sweden. There, in the bitter Nordic winter, he caught pneumonia and died in 1650. He was 54.
Descartes tried to bring about two revolutions in his lifetime. One of them was epistemological: he tried to base his philosophy on simple ideas that his readers could discover for themselves, rather than dogmas that had been handed down through the centuries. The other revolution was in metaphysics: Descartes described the world in terms that fit with the new mechanical, mathematical science of the world ushered in by Galileo. These revolutions also helped to shape his moral and religious philosophy, which we shall examine in Chapter 2.

The Meditations

We can begin our examination of Descartes’s philosophy by basing it on his Meditations on First Philosophy (1641). The Meditations is written like a guidebook meant to help any pilgrim blessed with common sense to arrive at the most fundamental philosophical truths. So this also makes it a good introduction to his philosophical system. We shall begin by following its presentation loosely, and then we shall explore various other regions of his philosophical worldview as they present themselves.
First, though, a word about Descartes’s style in the Meditations. It is not a work in which Descartes simply lays out what he thinks is true. Rather, the work recounts his discoveries as he meditates on his beliefs about the world. It is a chronicle of his discoveries, like an experimental log. There is a lot of give-and-take; Descartes will assert something, then doubt it, think further, and then embrace the conclusion for reasons quite different from those originally given for it. We shall not chronicle this give-and-take (or “dialectic”) style of the work, although it is an elegant portrayal of the way in which philosophical reflection takes place.


In the Meditations, Descartes tries to determine what he really knows. He realizes that he has been taught many things that he has later discovered to be false, and he wants to know whether he can settle once and for all what is true. So, for example, he had been taught that the earth stood still, and the sun went around it; and now he believed (though was not quite willing to proclaim) that the earth revolved around the sun. Is there any way we can sort through all of our beliefs, and get rid of the ones that might be false? In order to begin this project, he looks for what he cannot possibly doubt. But how does one go about finding what is indubitable? What is it to doubt something? Is it enough to simply say “I doubt it”? That’s too easy. Instead, Descartes suggests that we use the following criterion to determine whether any claim (“X”) can be doubted:
X can be doubted = I can conceive some scenario (even one that seems outrageous and bizarre) in which X would be false, but I still would believe that X is true.
The criterion demands that, when we doubt something, we not only imagine some way that the claim we are doubting could be false, but we also explain why we would have come to believe that it were true. So, for example, we can doubt that “Human beings have travelled to the moon” by supposing that no humans ever went there, and by supposing that there has been some vast cover-up (with fake film footage and so on) to make it seem to everyone that humans have walked on the moon. Descartes pushes this strategy to the limit, since he wants to find what cannot possibly be doubted. That is, any possible scenario counts – even one that no one takes seriously.
Using this criterion, he succeeds in doubting everything that our senses have ever told us – everything we have ever seen, heard or read. He does this by suggesting the scenario that our experience has been only a dream. Suppose we are dreaming, and have been dreaming our whole lives; if so, then we cannot trust anything we have seen, heard or felt. All of our experience would be an illusion, cooked up perhaps in our subconscious. Of course, it does not seem to us now that we are dreaming; but then again, that is how it is in dreams, isn’t it? It never seems to us that we are dreaming, even when the most outlandish things are happening. So the mere feeling that we are not dreaming does not prove anything.
But Descartes has not finished yet. He thinks there are some truths that we would still know even if we were dreaming. For our dreams, he observes, are not purely random noise. They are weird, to be sure, but they make some sense. Objects usually move around in the way that we think they do in waking life; there are relations between causes and effects; and the basic geometry and arithmetic of the world remain constant. In short, the dream world is still much like the waking world, in some fundamental ways, even if some strange things are happening in it. Perhaps if we are dreaming we cannot be sure of the particulars of our experience; but even if we are dreaming we can still be sure about these more fundamental features of experience. Or can we?
Descartes manages to doubt these more fundamental features by suggesting that, for all we know, there is some vastly powerful being (like God) who has power over our minds, and who is capable of making certain features and facts appear to be fundamental and true when really they are arbitrary and false. This great deceiver could make it seem obvious to us that unaffected bodies retain their shapes and that 2 + 3 = 5 when the truth is something much weirder and unimaginable. If we take seriously this scenario of a godlike being intent upon deceiving us, then Descartes argues that we can doubt even those things that seem to us most clearly and distinctly to be true. And at this point, we cannot rule out this scenario; it seems possible after all, though frightening and bizarre (not to mention paranoid).
At this point, Descartes thinks he has reached a limit, and has doubted everything he can. The question, though, is whether anything is left standing. Let us imagine that our experience is entirely at the mercy of some vastly powerful entity, who makes us have experiences that do not match up at all with how the world really is. In that case, is there anything that is wholly indubitable?


In the second meditation, Descartes finds one such indubitable truth: “I exist.” For I can conceive no scenario, no matter how bizarre, in which “I exist” would be false but I would still believe it to be true. Descartes is certain of his own existence because any act of thinking or doubting on his part presupposes his own existence, at least as a thinking thing. So long as he is thinking, he knows he exists. Not even God could deceive a nonexistent being into thinking it exists when in fact it does not – for there would be no one to deceive! This insight is often referred to among philosophers as “the cogito”, which is shorthand for the Latin sentence cogito, ergo sum – “I think, therefore I am.”
Is the cogito valid? It may seem to us perfectly obvious that a nonexistent being cannot be deceived about anything – but what guarantees this insight? If God can deceive us about the apparent truth of 2 + 3 = 5, why could God not also deceive us about the cogito? Descartes can reply that the cogito is genuinely different from the claims that we doubted under the deceiving-God scenario. It simply is not genuinely possible for us to conceive a scenario in which we are deceived into thinking we exist. We can mouth the words “Maybe I really do not exist but I still falsely believe that I do,” but it is impossible to take the idea seriously – we keep bumping into ourselves. This is basically what Descartes says in the Principles of Philosophy: “For it is a contradiction to suppose that what thinks does not, at the very time when it is thinking, exist” (AT VIIIA, 7). Trying to deny the cogito brings about not exactly a logical contradiction, but a kind of performative contradiction, like saying out loud, “I have lost my voice.” Saying it makes it false. We do not encounter this kind of contradiction when we try to doubt that 2 + 3 = 5 or that squares have four sides, since we can conceive of being deceived into thinking these claims are true when they are not. But we cannot imagine being deceived into believing the cogito when it is false. (Just try it!) So the cogito, unlike these other claims, escapes from the “God is deceiving me” scenario, and indeed any such scenario. By Descartes’s criterion, the cogito is indubitable.
Later, in the third meditation, Descartes claims that the cogito is shown to him by something he calls the natural light. “Whatever is revealed to me by the natural light – for example that from the fact that I am doubting it follows that I exist, and so on – cannot in any way be open to doubt” (AT VII, 46). He does not explain exactly what this natural light is, but it seems to be the “light of reason”, or what we can be sure of just in virtue of being rational beings. To be rational is to have a special capacity, and this capacity reveals the truths known through the natural light. We might put it this way: if we assume that we do have reason – that we are not completely insane – then we can be sure of certain rational truths, like the cogito and whatever else is shown by the natural light. And if we doubt our own sanity, then we really cannot be sure of anything at all. (This last doubt, that we might be insane, is a doubt Descartes never takes seriously.)
Thus Descartes believes there are some truths that are indubitable and are known just in virtue of our being rational; they are known independently of any particular experience. These truths, Descartes goes on to explain, are based on ideas we are born with, ideas that are innate. The most important innate idea, according to Descartes, is the idea of God. This is an idea we should explore at this point.


The cogito does not show much; only that I exist. And this “I” that exists, says Descartes in the second meditation, is only a thinking thing; we do not know for sure that it is connected to any kind of body, or even that there is anything else that exists. It could be a disembodied spirit floating in the void, for all we know. The “I” has experience – that is to say, it seems to see things, encounter things, perceive things, and think of things – but by the beginning of the third meditation we have no reason for thinking that this experience is veridical. In other words, we have no reason for believing that any of these things we think about really exist.
In the third meditation, Descartes argues that we have reason to believe that the “I” is not alone in the void. He argues this by carefully examining the ideas the “I” has, and figuring out whether the “I” itself could be the cause of them all. His hope is that he might come across some idea that the “I” could not have caused by itself, since then he would have good reason for believing that something else exists – namely, the cause of that idea, whatever it is.
This strategy will work only if Descartes knows what it takes for something to be the cause of an idea. He thinks he does, and we may call it the causal adequacy principle:
The cause of any idea must itself be sufficient for producing everything that is in the content of that idea.
Or, in Descartes’s terminology, the cause of any idea must have at least as much form...

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Citation styles for Understanding Rationalism
APA 6 Citation
Huenemann, C. (2014). Understanding Rationalism (1st ed.). Taylor and Francis. Retrieved from https://www.perlego.com/book/1666643/understanding-rationalism-pdf (Original work published 2014)
Chicago Citation
Huenemann, Charlie. (2014) 2014. Understanding Rationalism. 1st ed. Taylor and Francis. https://www.perlego.com/book/1666643/understanding-rationalism-pdf.
Harvard Citation
Huenemann, C. (2014) Understanding Rationalism. 1st edn. Taylor and Francis. Available at: https://www.perlego.com/book/1666643/understanding-rationalism-pdf (Accessed: 14 October 2022).
MLA 7 Citation
Huenemann, Charlie. Understanding Rationalism. 1st ed. Taylor and Francis, 2014. Web. 14 Oct. 2022.