Rene Descartes was the first of three pre-eminent Rationalist thinkers who appeared in the 17th century (the other two being Spinoza and Leibniz). Rationalism refers to a method of understanding the world that values reason over experience, maintaining that it is precisely through experience that we are led into error and confusion. Rationalism is contrasted with another philosophical approach to knowing the world, Empiricism.
The Father of Modern Philosophy
Descartes is quite rightly considered the father of modern philosophy because he was one of the first philosophers to employ the rigor and certitude of mathematics as a model for establishing solid philosophical principles that could therefore partake in that certitude. Indeed it has been said that one of his central aims was to ‘mathematise’ philosophy. He was also quite clear that science required philosophical foundations to be valid, affording philosophy a position of some central importance, a claim not so many scientists would agree with these days. Descartes thought philosophy was so important because, while science could describe the world and had immense practical value, it was useless unless we could know with certitude that its content (i.e. the objects in the world) actually existed, meaning the propositions of science would not just be useful, they would also be true. In other words, it is no good for science to tell us at what temperature water boils if we can’t be sure that the water exists in the first place.
He is a pivotal figure in the history of philosophy for a couple of reasons. First, he lived at a time when science was only just separating itself from philosophy (prior to this, all ‘science’ was studied under the umbrella of philosophy, Aristotle being the perfect example of this) and beginning to assert itself, through mathematics, as a powerful force. Secondly, Descartes, although a Christian who made it clear that he completely acquiesced to the authority of the clergy, was at the same time a (perhaps unwitting) key player in the vanguard of a revolution that would eventually see reason and free enquiry overcome the myth and supernaturalism which the very clergy he cherished so, branded.
Descartes’ whole philosophical project was about ensuring that our knowledge is true and certain. With that in mind, and his recognition of mathematics as the subject par excellence regarding indubitable truth, he sought to erect a general method that would allow him to ‘borrow’ the deductive certainty of mathematics and apply it to philosophy.
Descartes’ method comprises four principles he applies to all his future investigations, the outcome of which he believes will be true and certain knowledge:
1. Only accept as true what is presented to the mind so clearly and distinctly that it can no longer be doubted
2. Divide the problem into as many parts as possible
3. Begin with the simple and progress little by little to the more complex
4. Be thorough, omitting nothing from scrutiny
Cogito Ergo Sum
This phrase, ‘I think, therefore I am’, is almost certainly the most well-known utterance in all of philosophy. How did Descartes get to it and what is its significance?
First, Descartes resolves to doubt everything that he thinks he knows to be true. After all, his senses regularly deceive him (as in the way objects far away appear smaller than they really are), he can’t know for sure he isn’t dreaming and, just in case you still think he ought to have true knowledge of at least some things, a “malignant demon” might be deceiving him about absolutely everything (a la The Matrix).
It would appear there is no way we can have any certain knowledge; we just have to hope we aren’t being deceived by a demon (or trapped in the Matrix). But then Descartes realises something; he is thinking, he is doubting. If he is thinking, even if he is wrong about everything, there must be a he that is currently thinking. And ironically, the very act of doubting everything gives him one thing he can’t doubt, namely, that he exists to doubt in the first place. Even if we take the most extreme possibility, a demon is deceiving him about absolutely everything, the sheer fact that the demon is deceiving him, must mean that he exists, or what is the demon deceiving?
To express this sentiment, Descartes coined the phrase, “I think, therefore I am” but he could equally have said, “I doubt, therefore I am” or even “I am being deceived, therefore I am”. All of these phrases capture Descartes’ central insight. So even if I can’t be sure about anything else in the world, I can at least be sure that I exist. That’s an important first step.
It’s important to point out here that even though the expression is worded, ‘I think, therefore I am’, this is NOT a logically deductive argument, as in premise A plus premise B, therefore conclusion C. In his Meditations on First Philosophy Descartes actually omits the ‘therefore’ leaving the phrase simply, ‘I think, I am.’ What is the significance of this?
If Descartes’ argument is a logical one then it means it depends on logic, but he has already said he is doubting absolutely everything in the world, including the validity of logic; after all the demon may be deceiving him about logically deductive arguments, perhaps they always return false conclusions, we can’t assume they don’t. Instead of being just another logically valid argument, ‘I think, I am’ precedes all arguments. In fact, it precedes all thought, being the ground of thought itself. Without existence, there can be no thought, there can be no doubt, there can be no deception. Perhaps the best way to think of them isn’t as two linked linear concepts; ‘A à B’ or ‘I think à I am’, but as two sides of the same coin. If there is thinking taking place, something MUST exist to be doing the thinking.
Clear and Distinct Perceptions
Having discovered an absolutely certain truth (I exist), Descartes then looks for a general principle, “the ground of this certitude”, that he can apply to other propositions, thereby guaranteeing their truth as well. Since nothing confirms the certitude of his one guaranteed truth (I think, therefore I am) beyond the fact that he clearly sees it to be true, he concludes, “I might take, as a general rule, the principle, that all things which we very clearly and distinctly conceive are true”.
This is one (although not the only) glaring weak point in Descartes’ philosophy. After promising to doubt everything he can’t be absolutely sure of, to then slip in the clause that anything he “clearly and distinctly” perceives must be true seems to be a significant lowering of the bar he himself had originally set.
Being clear that he exists, Descartes can now enquire as to his nature; what indubitable knowledge can he come to about this thing he is certain exists?
Previously, he had believed himself to be composed of a soul (whatever that is) and a body. Descartes notes that he (as this composite existing thing) can move, think, perceive, etc., but he never attributed these capabilities to his body and furthermore, maintaining his project of doubting everything he can’t be certain about, the demon could be deceiving him about his body. Since he can’t know for certain that his body exists, he must relegate its status to doubtful, which leaves him with the soul.
So what is the soul? It is clearly nothing like the physical body which can move, be nourished and perceive. It is instead, a thinking thing, i.e. a mind. I think, I (a mind) exist. And to be even more precise, a mind doesn’t just think; it also doubts, understands, affirms, wills, imagines, etc.
Descartes also offers another argument in support of this conclusion. He theorises that even though he can imagine there are no bodies or things in the world, just the act of imagining guarantees that he exists (I imagine, I exist), and if he were to stop thinking then even though all manner of objects actually exist in the world there would no longer be any reason to suppose he exists. On the basis of these two propositions he concludes that “I [am] a substance whose whole essence or nature consists only in thinking… so that… the mind by which I am what I am, is wholly distinct from the body, and is even more easily known than the latter”.
With this, Descartes effectively cleaved the world in two. He definitely wasn’t the first to do this, (Plato had thought the same and Christianity is wholly predicated on a distinction between the immaterial and the material) but after philosophy had become mired in Christianity for centuries, Descartes was one of the first to renew interest in this topic from a purely philosophical perspective, outside an explicitly religious context.
So, the world is divided into two substances, mind and matter, and he, the real Descartes, is composed of the former. There are two further points of interest here.
The first is that Descartes thought we could know our own minds more easily and completely than we could our bodies, or matter in general. The reason he thought this is that he recognised that perception (in the full sense of the word, i.e. the actual understanding of brute sensations) is nothing to do with our senses but is rather an exercise of the mind. When we perceive a table in front of us, we might be tempted to think that reveals something first and foremost about the table or our sensory organs (both forms of matter) but Descartes is claiming that since it is only through the intellect that we can know the corporeal world, what we actually have direct knowledge of first and most clearly is the mind.
The second point is that, in direct opposition to Plato, the mind is not “lodged in the human body exactly like a pilot in a ship… but that it is necessary for it to be joined and united more closely to the body”. Descartes would later come up with the fairly untenable proposition that the mind is joined to the body at the point of the pineal gland in the brain. Exactly how the soul is “lodged in the human body” remains something of a fairly hazy point in Descartes’ philosophy and leads to what is really a knock-down argument against him.
As I have already intimated, one huge, and I think ultimately insurmountable, problem arises at this point. That is explaining exactly how something immaterial (the mind) can possibly be “joined and united” to something material (the body) and how the one can exert any kind of influence on the other. By definition, something immaterial lacks any physical component (and vice versa), so it seems logically impossible that it should be able to interact at all with something physical. Even postulating the existence of God (as Descartes will do momentarily) fails to overcome this objection.
Descartes was a Christian and believed in the existence of the Christian God. He gives three ‘proofs’ of this:
1. The first cosmological argument. Cosmological arguments attempt to infer the existence of God from certain facts about the world. This version of the cosmological argument requires that one accept a Scholastic idea that has little relevance today, namely that there must be at least as much reality in the cause as in its effect (i.e. what ‘is’ cannot be produced by what ‘is not’, and the less perfect cannot be the cause of the more perfect). Descartes slips this ‘truth’ past his method by claiming that he knows it indubitably through the “natural light”, which appears to achieve the same job for him as the notion of “clear and distinct” ideas does.
If you can accept this, the rest of the argument falls into place relatively painlessly. Descartes has in his mind the “clear and distinct” idea of God, i.e. a Perfect Being. But since Descartes himself is quite clearly imperfect, this idea couldn’t have possibly originated from him. The idea of a perfect being must have therefore come from a Perfect Being, therefore God exists.
2. The second cosmological argument. In this argument Descartes wonders if he could exist without God. He knows he didn’t create himself (if he had, he would then have perfect knowledge; an idea that is clearly false) and he rejects the idea that he could have always existed as he is now (this is because Descartes thinks that each part of his life is completely independent of any other so existence in the past doesn’t guarantee existence in the future). Therefore the fact that he (Descartes) exists is clear evidence that he must have been created by a Being capable of such things, i.e. God.
3. The ontological argument. Ontological arguments attempt to show that existence itself is necessarily included in the concept of God. Descartes claims just this. As soon as he thinks of God, he cannot help but attribute all manner of perfections to Him and one of those perfections must necessarily be existence (for how can anything be perfect if it lacks something as basic as existence?).
Descartes then uses this idea he has of God as containing all manner of perfections to extract some ‘truths’ about His nature. Since properties like sadness, doubt, etc. are all imperfections, they can’t be a part of God. Moreover, since “all composition is an evidence of dependency, and… a state of dependency is manifestly a state of imperfection”, God cannot be composed of two natures, i.e. mind and body, but rather must be some kind of immaterial intelligence or mind.
Descartes cannot quite rest here though; he must identify one more aspect of God that will turn out to be absolutely crucial to his project. Descartes considers deceit to be a form of imperfection and since God is a completely Perfect Being (as revealed in his clear and distinct perceptions of Him), He is no deceiver.
It is worth pointing out that Descartes employs a little bit of circular reasoning here, claiming that he can believe in the truth of his “clear and distinct” ideas because God, as a non-deceiver, wouldn’t lead him astray about those. This is circular because to get to his conclusion in the first place that God is no deceiver, Descartes already had to make abundant use of his “clear and distinct” idea of God as a Perfect Being.
The External World
So, after starting out doubting everything; Descartes now knows that he exists, he is a mind (a thinking, willing, etc. thing), God exists, and God is no deceiver. But this won’t give him the foundation he needs to guarantee the truth of scientific discoveries, which are ultimately about objects in the external world.
Fortunately, knowing that God is no deceiver gives Descartes all the ammunition he needs to demonstrate that, even though we are sometimes wrong about our sensations, we have the ability to detect these errors by following Descartes’ method and relying only on “clear and distinct” ideas, which are ultimately guaranteed by our non-deceiving God to be true.