René Descartes was a French 17th century philosopher, famous above all for saying 'I think therefore I am', but worthy of our attention for many reasons beyond this. What makes him stand out is that he was a fierce rationalist. In an age when many philosophers still backed up their arguments with appeals to God, Descartes trusted in nothing more than the human power of logic. This is how he defiantly kicked off his book 'Rules for the Direction of the Mind': 'I shall bring to light the true riches of our souls, opening up to each of us the means whereby we confined within ourselves, without any help from anyone else, all the knowledge that we may need for the conduct of life.' Descartes had immense faith in what introspection guided by definition, sound argument, and clarity of thought could achieve. He believed that much of what was wrong with the world was caused by misusing our minds by confusion, bad definition, and unconscious illogicality. His life was an attempt to make our minds better equipped for the task of thinking. To solve key questions, Descartes proposed that one always had to divide large problems into small, understandable sections by way of incisive questions. This is what he called his 'method of doubts'. We get muddled by certain questions like 'what's the meaning of life', or 'what is love?', because we're not careful enough about how we break these big inquiries down. He described the method of doubts as akin to having a large barrel of apples where good ones are mixed with bad ones. To be a philosopher means a commitment to sorting out the entire barrel to inspecting each apple Individually and throwing away all the bad ones to ensure only those of the best quality are left. Another way to think about Descartes, and this explains why he would among other things, turn out to be such a hero to the leaders of the French revolution, is that he believed in grounding all of our ideas in individual experience and reason, rather than authority and tradition. In his greatest book 'Discourse on the Method' published in 1637, he explained how he had come to write it: 'A long time ago, I entirely abandoned the study of letters resolving to seek no knowledge, other than that which could be found in myself or else in the great book of the world, I spent my youth traveling visiting courts and armies, mixing with people of diverse temperaments and ranks gathering various experiences, testing myself in situations which fortune afforded me, and at all times reflecting personally upon whatever came my way so as to derive some profit from it.' Descartes spent a large part of his adult life away from his native France in the Dutch Republic, since he held the belief, not entirely unwisely, that the mercantile Dutch would, as a people, be far too concerned with earning money to pester a free-thinking man like himself. However it turned out that the Dutch were a little less materialistic than he'd hoped, and the philosopher ended up moving 24 times to keep ahead of spies and government agents. Descartes' subjective approach to philosophy reached its climax when he arrived at the famous phrase 'Cogito ergo sum' —'I think therefore I am'. The phrase first appeared in French—'Je pense donc je suis'—in the Discourse on the Method before then appearing in Latin in the Principles of Philosophy of 1644. It was intended to be Descartes' ultimate answer to a question that philosophers sometimes get perhaps unreasonably interested in, namely 'How can one know that anything including oneself, actually exists rather than being some sort of dream or phantasm?' On his quest was certainty around this question of whether it might all be a dream Descartes began by observing that our human senses are deeply unreliable. He couldn't, for example, he said, be trusted to know whether he was actually sitting in a room in his dressing gown next to a fire, or merely dreaming of such a thing. But there was one thing he could know for sure: he could trust that he was actually thinking. His existence could be proved by a neat tautological trick. He could not be thinking and wondering if he existed if he did not exist, therefore his thinking was a very basic proof of his being or to return to the maxim 'I think therefore I am'. This might not sound like a huge insight, but Descartes used it as an Archimedean point in an epistemologically unsteady world. With this certainty safely banked, Descartes argued that his mind could go to discover other similarly irrefutable truths. Some of the charm of Descartes' work comes through his entwining of personal details, along with more arid philosophical passages. He tells us, for example, that his revolutionary idea came to him during the winter of 1619, when he'd escaped the fierce cold of the low countries by hopping into a stove and spending the whole day meditating inside. Descartes epitomizes the solitary end of philosophy. One can, in his eyes, solve the most profound problems by searching deep within oneself. Teams of individuals, or ideas passed through the generations as they are in universities are deeply suspect for Descartes. Philosophers don't need gangs of scientists using expensive equipment, unheard-of terminology and huge datasets. They just need a quiet room and a rational mind. At another point, Descartes recounts that he mocked friends of his who once showed up at his home at 11 in the morning and was surprised to find him still in bed. 'What are you doing?' they inquired skeptically. 'Thinking,' Descartes replied. The group was stunned, but Descartes criticized them in turn for privileging often nonsensical practical tasks over the beauty of pure quiet reflection in bed. In 1649, Descartes finished another great work: 'Passions of the Soul'. It was the outcome of six years of correspondence with a royal acquaintance, the Princess Elizabeth of Bohemia, who was a keen amateur philosopher, and a rather emotional and turbulent soul. She had written to Descartes begging him to write about passions in order that she might get to know and control her own more clearly. Descartes obliged. Thinking that the ancient philosophers had done a poor job of analyzing the passions and that ordinary and not-so-ordinary people would benefit immensely from another look at the topic, he therefore opened the Passions of the Soul with a characteristic claim: 'I shall be obliged to write just as if I were considering a topic that no one had dealt with before me.' The word provides a beautiful taxonomy of pretty much any passion one might feel, as well as descriptions of their causes, effects, and functions. This is followed by another section called 'The Discipline of Virtue', a manual of advice on how we can control our passions and enjoy a virtuous life. Descartes identified six fundamental passions: wonder, love, hatred, desire, joy, and sadness. From these they're followed in his eyes an unlimited number of specific passions; combinations of the original ones. Descartes didn't believe in vanquishing passions as the ancient stoic philosophers had proposed, merely in learning how to identify them in oneself and understand their impact on one's behavior. He would have been very sympathetic to psychotherapy. He believed that a key task of being a philosopher was to help people understand and therefore control their passions; that is, become a little less anxious, status-driven, scared, or inclined to fall head over heels in love with inappropriate people. He was optimistic about how much progress we could make psychologically. Even those who have the weakest souls can acquire absolute mastery over their passions if they work hard enough at training and guiding them. Descartes' psychological and philosophical work attracted ever more powerful admirers. In 1646, Queen Christina of Sweden got interested in sorting out issues in her mind and began a correspondence with Descartes. She even persuaded the philosopher to move to Sweden to tutor her in passion and philosophy in 1649. However, the early working hour was required. the queen could only make time for lessons at 5:00 a.m., and the harsh cold soon made Descartes ill. He died of pneumonia in 1650 at the age of 53. To remember Descartes by 'I think therefore I am' is perhaps not as shallow as one might initially have presumed. The sentence does truly capture something important about him and the task of philosophy in general. It signals a commitment to working through emotional confusion, prejudice, and unhelpful tradition, in order to arrive at an independent rationally founded vision of existence.