Rene Descartes

Rene Descartes
Rene Descartes is deemed as the “Father of Modern Philosophy.”

Welcome to our topic Rene Descartes! This is our first topic for the Midterm Period. Rene Descartes, as we all know, is a very important figure in the history of philosophy. He is the founder of the philosophical movement called Rationalism in the modern age. This period marks the continuation of our study on the history of philosophy. We had just moved on from the Medieval Period into the Renaissance Period. Rene Descartes is no longer a stranger to most of you. You have already met him in various situations and capacities being engineering students you are. Hence, let us take a closer look at the man and philosopher who revolutionized the philosophical way of thinking at the turn of 17th century.

“If we begin with certainty, we will end with doubt; If we begin with doubt, we will end with certainty.”  ~ Rene Descartes

Intended learning outcome

At the completion of this topic, you should be able to:

  1. Explain the influence of the dualistic ideas of Descartes and his contributions to the modern philosophy of metaphysics and epistemology.

Who is Rene Descartes?

Rene Descartes was born in France in 1596. He received an excellent education at the hands of the Jesuits, an education which included philosophy and mathematics; then he took a degree in law at the University of Poitiers, his home town. As a brilliant student he perceived that many of the arguments put forward by the various authorities he was studying were invalid, and often he did not know what to believe. In order to complete his education, he says, he joined the army, and traveled widely in Europe as a soldier, though without seeing any fighting. His travels taught him that the world of human beings was even more varied and mutually contradictory than the world of books. He became obsessed by the question whether there was anything we could be sure of, anything we could know for certain.

Rene Descartes settled down in Holland, which allowed the greatest freedom of expression of any country in Europe, and proceeded to examine the foundations of human thought, his investigations taking the form of philosophy, mathematics, and science. For roughly the twenty years between 1629 and 1649 he produced original work of the highest quality. In philosophy his outstanding works were two: Discourse on Methods, published in 1637, and Meditations, published in 1641. In 1649 Queen Christina of Sweden invited him to Stockholm to tutor her in philosophy. In the bitter Swedish winter he contracted pneumonia, and died in 1650.

Methodic doubt

Rene Descartes was a mathematician of genius, and invented a new branch of the subject which consists in the application of algebra to geometry: it is known variously as analytic geometry or coordinate geometry. He also invented the graph. Those two familiar lines on a graph are named after him: they are called Cartesian coordinates, the word Cartesian being the adjective from the name Descartes. Descartes first carved a niche for himself in the pantheon of intellectual giants by discovering analytical geometry, thereby fulfilling the old Pythagorean dream of demonstrating the relation between plane geometry and pure algebra.

The transparent and utterly reliable certainties of mathematics thrilled him. And he began to wonder whether what gave mathematics its certainty was something that could be taken over and applied in other areas of knowledge. If it could, we would have a ready refutation of the skeptics who maintained that nothing else could be known for certain. Skepticism is a philosophy which maintains that nothing could be proven with utter certainty for there will always be new ideas to emerge to refute and contradict existing ideas. But, far more important than that, we would have at our disposal a method for acquiring certain knowledge about the world, a method on the basis of which science in the modern sense could be constructed.

Descartes came to the conclusion that mathematics owed its certainty to the following set of reasons. Mathematical demonstrations began from a minimal number of premises of the uttermost simplicity, simplicity so basic and so obvious that it was impossible to doubt them, such as that a straight line is the shortest distance between two points. The demonstrations then proceeded deductively by one logical step at a time, each step being irrefutable, and usually very simple, again indubitable. And then – the thing that entranced everyone who came under the spell of mathematics – you found that in moving only by logical steps, each of which was simple and obvious, from premises each of which was also simple and obvious, you began to reach conclusions that were not at all simple and not at all obvious: whole worlds of unanticipated discoveries started opening up before you, many of them amazing, many of them of great practical usefulness, and all of them reliably true. And there seemed to be no end of these undiscovered worlds: mathematicians were for ever opening up the way to unexpectedly new ones, as Descartes himself had done.

Now, asked Descartes, might it be possible to apply precisely this method to non-mathematical knowledge? If we can find any propositions outside mathematics whose truth it is literally impossible to doubt we can use them as premises for deductive arguments, and then whatever we can logically deduce from them must be true. This will give us the methodological foundations for a body of knowledge on whose discoveries we can one-hundred-percent rely. But are there any such premises? Or is it the case (as many people in Descartes’ own day were saying) that nothing at all can be known for certain outside mathematics and logic?

In his search for indubitable premises, Descartes journeyed through three stages. First, he considered the experience of direct and immediate observation. If I look head-on at this church spire, or that tree dipping in the water, surely I can trust the immediate evidence of my senses? Alas, on investigation it turns out that direct observation deceives us frequently. This church spire that flashes golden in the noonday sun, and glows red at sunset, looks grey the rest of the time. That branch that looks bent at the point where it enters the water turns out to be straight when I lift it out. So I can never be sure that things are in fact as they appear to me, however head-on I may be looking at them, and however awake and alert my state of mind.

Malicious demon

This brings us to Descartes’ second set of considerations. Often, he says, he had believed himself with complete certainty to be doing something or other, and then woken to find that he had been dreaming. Sometimes these dreams had been homely dreams about his everyday activities: he had dreamed he was sitting at his fireside reading or at the desk in his study writing, when all the time he had really been in bed sleeping. How could he be sure he was not dreaming at this very instant? By this token it appeared that he could never be absolutely sure he was not dreaming, or hallucinating, or something of that sort.

At this point of apparent despair in his search for indubitability, Descartes gave the knife an additional and malign twist, and this was his third phase. Suppose he said, that all the errors and illusions on my part were due to the fact that there exists, unknown to me, a higher spirit whose sole aim is to deceive me, and who can exercise superhuman powers over me, can make me sleep and dream vividly that I am awake, or make everything I look at look to me as something else, or make me believe that two and two are five. Is there anything at all about which even a malignant spirit such as this would be unable to deceive me? And he comes to the conclusion that there is, namely the fact that the deliverances of my consciousness are whatever it is they are. I can always make false inferences from them – I may suppose myself to be sitting beside a fire when in fact there is no fire and I am in bed dreaming, and yet that I suppose myself to be sitting beside a fire is an inescapable fact.

So the one thing in this and every other case that I can be unshakably sure of is that I am having the experiences I am having. And from this there are things I can infer with absolute certitude. First of all it means I know myself to be some sort of existing being. I may not know my own nature, indeed I may have completely mistaken views about what it is, but that I exist is indubitable; and what is more I know with absolute certitude that I am a being which at the very least, if nothing else, has conscious experiences; the particular conscious experiences I have. Rene Descartes encapsulated this conclusion in a Latin phrase that has become very famous: “Cogito, ergo, sum,” usually translated rather ineptly as “I think, therefore I am.”

Pursuit of certainty

So, Rene Descartes says, there actually are things outside mathematics and logic, things about the world of fact, which we can know with absolute certitude. But is there anything that can be inferred from those things with the same degree of certitude? At this point he uses a new version of an old argument, a new version of the ontological argument for the existence of God (Thomistic argumentative proof of the existence of God). I know myself, he says, to be a very imperfect being, ephemeral and perishable, and finite, and yet I have in my mind the concept of an infinite being, eternal and immortal, perfect in every way; and it is impossible that anything should be able to create something greater than itself out of its own resources; therefore this perfect being must exist, and must have implanted in me an awareness of itself, like a craftsman’s signature inscribed on an example of his handiwork.

The fact that I know that God exists, and is perfect, means that I can put my trust in him: he will not, unlike the malicious demon, deceive me. So provided I play my full part, pay serious attention, and do all the disciplined thinking required of me, I can be certain of the truth of whatever is then presented clearly and distinctly to me as being true – not by my senses, of course, which I already know to deceive, but by my mind, that part of me that apprehends God and also mathematics, neither of which the senses can do; the mind that I irreducibly am.

The birth of Rationalism

Out of this conclusion grew the school of philosophy known as rationalism, which bases itself on the belief that our knowledge of the world is acquired by the use of reason, and that sensory input is inherently unreliable, more a source of error than of knowledge. Rationalism has been one of the abiding traditions of Western philosophy ever since. Its greatest period spanned the 17th and 18th centuries, and its outstanding figures apart from Descartes were Spinoza and Leibniz, but it has never lost an important degree of influence on Western thinking.

Few of the great philosophers after Descartes shared his view of the indubitability of God’s existence. But he introduced some fundamental things into Western thought. His belief that the logic of scientific discovery required us to start from indubitable facts and then derive logical consequences from these facts in chains of deductive reasoning became foundation to Western science. Subsequent thinkers came mostly to believe that controlled and disciplined observation (and therefore the use of our senses) had an indispensable role to play in establishing those indisputable facts that we need to stock our premises, but they still thought that Descartes had got the basic method right, namely, to start from reliable facts, then apply logic to those facts and not to let anything intervene that is in the very least degree susceptible to doubt, no matter how far-fetched that doubt might be. Rene Descartes convinced people that this method made possible a mathematically based science that would give human beings reliable knowledge about the world, and indeed that it was the only way of finding out about the world with absolute certainty.

Rene Descartes and the principle of dualism

Rene Descartes concluded that what human beings irreducibly led him to develop a view of the world as consisting ultimately of two different kinds of substance, namely mind and matter. He saw human beings as experiencing subjects whose world, apart from themselves, consists of material objects which they observe. This bifurcation of nature into two kinds of entitymind and matter, subject and object, observer and observed – became a built-in part of Western man’s way of looking at the world. To this day it is referred to by philosophers as “Cartesian dualism.”

Between Rene Descartes and the 20th century there were few leading philosophers who dissented from it, perhaps the most effective being Spinoza and Schopenhauer Only in the 20th century did dissent from it become widespread – and even then it was by no means universal; some leading philosophers continue to subscribe to it. Even more than Francis Bacon and Galileo, Rene Descartes was a key figure in persuading people in the West that certainty was available in our knowledge of the world. To obtain it you needed to follow the right method, but if you did that you could build up an impregnable science that would give you rock-hard, reliable knowledge. He, more than anyone else, “sold” science to educated Western man. It was largely under his influence that the pursuit of certainty came to dominate intellectual activity in the West, and that considerations of method became central to that pursuit, for he regarded himself not as giving us such knowledge with certainty but as showing us how to get it.

It will be remembered that the earliest philosophers, the Pre-Socratics, had taken their fundamental question to be; “What is there?” or “What  does the world consist of?” Socrates had replaced this with a different question, namely “How ought we to live?” These questions and their derivations dominated philosophy for many hundreds of years. But then along came Rene Descartes and displaced them with one that was different yet again: “What can I know?” It put epistemology, which is the theory of knowledge, at the center of philosophy, where it remained for three hundred years, so much so that many subsequent philosophers came to think of philosophy as being, essentially, epistemology.

Descartes’s legacy

For this reason Rene Descartes is generally thought of as the first modern philosopher, and it often happens that students going to university to study philosophy are required to begin their course with his work. There is another reason for this.

By using doubt as a method – systematically suspending commitment to anything that it is logically possible to doubt, thereby stripping away layer after layer of our accustomed ideas and suppositions – he takes us right back to square one, and attempts to begin again from scratch.

The first-person-singular form of the question sharpens its cutting edge – not “What is it possible for us human beings to know?” but “What can I know?”  This appeals to the young, and rightly so.


  • Dorling Kindersley. (2011). The Philosophy Book. New York: DK Publishing.
  • Stumpf, Samuel Enoch. (2008). From Socrates to Sartre and Beyond. New York: McGraw Hill Publishing.
  • Palmer, Donald. (2006). Looking at philosophy:The unbearable heaviness of philosophy made lighter 4th Edition. New York: McGraw Hill Companies.
  • Ramos, Christine Camela. (2004). Introduction to Philosophy. Manila: Rex Bookstore.
  • Gaarder, Jostein. (2004). Sophie’s World. Great Britain: Phoenix House.
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