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His Life, Character, and Philosophy

Modern philosophy began in the warmth of a cockle stove, with three visions.

René Descartes (1596–1650) is often called the father of modern philosophy. The title owes less to any single doctrine than to the ambition of his project. As the old Aristotelian worldview collapsed under the weight of the Scientific Revolution, Descartes set out to rebuild human knowledge from the ground up, in a way that could accommodate God, the soul, and human freedom.

A World Crying Out For a Philosopher

The demise of the Aristotelian system, brought about by the Copernican and Scientific Revolutions, left a void that needed filling—ideally by some all-encompassing metaphysical system on the scale of the old, Aristotelian one. If the Earth no longer stood at the centre of the cosmos, was man not the glory of creation, as affirmed in the Bible (1 Corinthians 11:7)? In this new mechanistic, atomistic world of matter in motion, where might God and the immaterial soul fit in? Where freedom and justice? And where, even, heaven and hell?

As recently as 1588, Galileo, qua mathematician, had been invited to address the Florentine Academy on the location, size, and arrangement of hell as described in Dante’s Inferno—underscoring the scale of the mind shift required. Even that paragon of the Scientific Revolution, Newton, albeit in secret, dedicated the larger part of his life to alchemy and the search for the fabled philosopher’s stone.

The three seventeenth-century philosophers who rose to the challenge of formulating a comprehensive metaphysics are René Descartes (1596–1650), Baruch Spinoza (1632–1677), and Gottfried Wilhelm Leibniz (1646–1716), who sometimes inserted, with little to no justification, the nobiliary particle von in front of his cognomen.

Three Visions in a Stove-Heated Room

Descartes categorically rejected the substantial forms and primary matter of the mediaeval, Aristotelian schoolmen. In a letter to his friend Marin Mersenne dated 28 January 1641, he writes that his Meditations on First Philosophy ‘contain all the foundations of my physics. But please do not tell people, for that might make it harder for the supporters of Aristotle to approve them. I hope that readers will gradually get used to my principles, and recognise their truth, before they notice that they destroy the principles of Aristotle.’

Two decades earlier, Descartes had been serving in the army of Duke Maximilian of Bavaria. On 10–11 November 1619, while stationed near Ulm or else Neuberg an der Donau, he found refuge in a room with an ‘oven’ (probably a cockle stove) to escape from the cold and reflect on his thoughts. That night, he had three dreams which determined the course of his life. To repay these visions, he vowed to make a pilgrimage to the shrine of Our Lady of Loretto in the Italian region of Marche—and, in 1623, fulfilled his vow.

What Descartes had seen or grasped on that eve of St Martin’s Day 1619 is the unity of the sciences under mathematics: if a concrete problem could be abstracted into mathematical form, it would become clearer and more amenable to solving. Thus, in the course of his life, he contributed several mathematical innovations. In his La Géométrie (1637), he introduced the modern exponential notation which is taught in every contemporary school. He established the convention of using the letters x, y, z to represent unknown variables in equations, and a, b, c to represent known variables. If that were not impressive enough, he bridged algebra and geometry by transforming numerical relationships into geometrical shapes, plotting these lines and curves on a coordinate plane, and showing how they could be represented in the form of algebraic equations—a field now known as analytic, coordinate, or Cartesian geometry.

Descartes sought to carry the certainty of mathematics into philosophy itself. The culmination of that lifelong project was the Meditations on First Philosophy, which laid the foundations of his new metaphysical system while quietly dismantling that of Aristotle.

The Method of Doubt (Dubitatio methodica)

The closed-in stove-heated room later came to symbolise Descartes’ famous method of doubt, by which he systematically dismantled the edifice of his beliefs to rebuild on a more secure foundation of indubitable truths, to be arrived at through a predetermined set of logical rules.

In this climate of radical doubt, he could doubt the existence of the outside world, even the existence of his own body—but not that he was the one doing the doubting. This insight is encapsulated in his famous dictum, Cogito, ergo sum (‘I think, therefore I am’). The very act of doubting presupposed a thinking self to do the doubting.

Although Descartes knew that he was thinking, and so that he was, he could not be sure that his thinking bore any relation to the outside world. So he introduced an a priori proof (a proof derived from thought alone) for the existence of God, and argued that such a benevolent being would not deceive his favoured creation, man—so long as man had employed his (Descartes’s) method of doubt and taken every precaution to have ‘clear and distinct’ ideas and not to be deceived.

Dualism and the Piece of Wax Analogy

The Cogito also transformed Descartes’ understanding of reality. The indubitability of the thinking self led him to conclude that mind and body must be fundamentally different kinds of substance. The defining attribute of the mind (or soul, or res cogitans) is thought, while that of the body (or res extensa) is extension. It is by the knowable mind, rather than the deceptive senses, that the physical can be apprehended.

Descartes illustrated this point with one of the most famous passages in the Meditations: the wax analogy. When a piece of wax is heated, all its sensory properties change. Only the mind grasps its underlying essence, which consists in extension (as well as flexibility and movability in space), and recognises it as the same piece of wax. The physical, being extended, is divisible; but mind is indivisible, and therefore not physical. Since it is not physical, mind is beyond the laws of physics, and free and immortal.

[T]here is a great difference between the mind and the body, inasmuch as the body is by its very nature always divisible, while the mind is utterly indivisible. For when I consider the mind, or myself in so far as I am merely a thinking thing, I am unable to distinguish any parts within myself; I understand myself to be something quite single and complete… By contrast, there is no corporeal or extended thing that I can think of which in my thought I cannot easily divide into parts; and this very fact makes me understand that it is divisible. This one argument would be enough to show me that the mind is completely different from the body. 

The Soul of Animals

Descartes’s mind-body dualism is commonly taken as the starting point of modern philosophy. His method is indeed revolutionary, but the substance of his philosophy is in fact an attempt to shelter God, man, and his immortal soul from the new mechanism. Thanks to Descartes, those who embraced the Copernican revolution could remain good Christians, or claim as much.

But in solving one problem, Descartes created several others, most notably the place of animals and the mind-body problem.

Under the Aristotelian system, all living things had a vegetative (or nutritive) soul; animals, in addition, had a sensitive soul; and humans, on top of that, had a rational soul.

For fear of granting them immortality and a place in heaven, Descartes denied souls to the animals. Animals, he claimed, are mere automata, whose functions ‘follow from the mere arrangement of the machine’s organs every bit as naturally as the movements of a clock or other automaton follow from the arrangement of its counterweights and wheels’.

For Descartes, it is not merely that animals do not reason, but also, contra common sense, that they do not feel, perceive, or sense. Clearly, he did not have a cat. According to lore, he once threw a cat out of a window in an attempt to demonstrate that the poor thing lacked consciousness.

The Mind-Body Problem

If mind and body truly are incommensurate, how is it possible for them to interact? How might my mind move me to write these words without violating, or else submitting to, the laws of physics? Conversely, how might my eyes and ears relay sense experience to my mind?

Descartes responded to this so-called mind-body problem in two ways. At times, he said, literally, ‘Only God knows.’ At other times, he suggested that mind and body interact at the pineal gland, on the grounds that this structure is mobile and central in the brain. But this only puts the problem at one remove, for the question then becomes, how is it possible for the mind to interact with the pineal gland?

The Philosopher’s Daughter

Although France’s most famous philosopher, Descartes spent the greater part of his adult life in the relative safety of the Dutch Republic. There, he met a servant called Helena who became the mother of his illegitimate daughter Francine (b. 1635), whom he passed off as his niece. When Francine died, aged five, of scarlet fever, he called it the greatest sorrow of his life, even stating that it was not unmanly to cry. Later, a legend arose that he—the philosopher who had compared living bodies to machines—constructed an automaton in her likeness.

The Tree of Life

The name René derives from the Latin Renatus, ‘born again’—fitting for the man who sought to rebuild philosophy from first principles. But although remembered as a philosopher, Descartes looked upon himself first and foremost as a natural philosopher (scientist) and physicist.

In the preface to his Principles of Philosophy (1644), he compared philosophy to a tree, with metaphysics as its roots, physics as its trunk, and the other sciences as its branches—and it is, of course, the branches that bear the fruit. 

The ‘other sciences’ could be reduced to three principal ones, medicine, mechanics, and morals—which is why, in 1649, he published a book on the emotions, The Passions of the Soul.  He sent a copy to his penfriend Queen Christina of Sweden, who was so impressed that she invited him to join her court.

In October 1649, he left Holland for Sweden. But the northern winter did not agree with him, and the frenetic Christina insisted on taking her lessons at five in the morning. He did not live to see the spring.

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His Life, Character, and Philosophy

Hume leading Rousseau to safety in England

David Hume was one of the greatest philosophers of the Enlightenment—and one of its most controversial. At a time when philosophers placed their faith in reason, he questioned everything from causation and the self to religion and morality. His radical scepticism led many to regard him as an atheist and cost him several university appointments. Yet the man whom many feared for his ideas was, by all accounts, open, sociable, and cheerful. Today, he is recognised as one of the most influential thinkers in the history of philosophy.

David Hume was born in 1711 in Edinburgh. His father Joseph was the laird of Ninewells, his mother Katherine the daughter of the Lord President of the Court of Session (Scotland’s supreme civil court). His father’s family was a cadet branch of the Earls of Home (pronounced ‘Hume’). In 1713, Joseph died at the age of thirty-three, leaving Katherine in sole care of three tots.

Hume went up to the University of Edinburgh at the age of ten or twelve, young even for the time, but found little of value in formal lectures. Later, he told a friend that ‘there is nothing to be learnt from a professor, which is not to be met in books.’ He shunned the legal studies that his family intended for him, preferring instead to devour classical and philosophical texts. ‘While [my family] fancied I was poring upon Voet and Vinnius, Cicero and Virgil were the authors which I was secretly devouring.’

This inner conflict drove him, at the age of eighteen, to a nervous breakdown. A local physician diagnosed ‘a disease of the learned’ and had the good sense to prescribe horse riding for outdoors and, for indoors, wine drinking, which worked a charm. Once Hume had found and embraced who he was, his malady never returned. In later life, he became an advocate of ‘ordinary life’ as a cure for ‘philosophical melancholy’.

I dine, I play backgammon, I converse … and whenafter three or four hours’ amusement, I would return to speculations, they appear so cold, and strain’d, and ridiculous, that I cannot find in my heart to enter into them any further.

A Treatise of Human Nature

In 1734, at twenty-three, Hume moved to Bristol to work as a clerk for a sugar importer. Ill-suited to the job, he soon left for Paris, then Rheims, then the small town of La Flèche, with its Jesuit college made famous for having schooled Descartes. Hume had been attracted to La Flèche by the college’s library of some 40,000 books, as well as the lower cost of living compared to Paris or Rheims. He remained in La Flèche for three years (1734-1737), during which he wrote A Treatise of Human Nature.

When it was published in 1739, the reception was not as Hume had hoped. In the short autobiography written near (almost at) the end of his life, he tells us that the Treatise ‘fell dead-born from the press, without reaching such distinction, as even to excite a murmur among the zealots.’ He disavowed the Treatise and asked that his more polished Enquiry Concerning Human Understanding (1748) be regarded as his final word—a request that posterity has ignored.

Essays Moral and Political

After his disappointment with the Treatise, Hume turned to essay writing, which was then in vogue. In 1742, he published the first volume of his Essays Moral and Political, which were favourably received and ‘soon made me entirely forget my former disappointment’.

Hume developed a talent for prose and a reputation as a skeptic and all-round heretic. In 1745, he applied for the vacant chair of moral philosophy at Edinburgh, but was rejected on the strength of his reputation. He took up the post of tutor and companion to the troubled and impossible Marquess of Annandale, but resigned after a year.

He then joined a planned expedition to Quebec, serving as secretary to Lieutenant-General James St Clair. However, the expedition was cancelled and the forces diverted to a raid on Lorient in Brittany. The failure of this operation did not prevent Hume from sporting the uniform of an officer on subsequent diplomatic missions with St Clair to the courts of Vienna and Turin (then the capital of Savoy).

History of Great Britain

In 1748, Hume’s re-write of the first volume of the Treatise of Human Nature was published as Philosophical Essays Concerning Human Understanding (retitled in 1758 to An Enquiry Concerning Human Understanding). After being turned down as an improper person for the Chair of Moral Philosophy at Glasgow, he became, in 1752, the Keeper of the Advocates’ Library in Edinburgh—affording him the time and resources to write his monumental, and monumentally successful, History of Great Britain, published in six volumes over eight years (1754-62). Hume became, in his own words, ‘not only independent, but opulent.’ Such was the success of the History that, in his lifetime and for a long time after, he was better known as a historian than a philosopher.

Rescuing Rousseau

In 1763, Hume became Secretary to the British Embassy in Paris. He basked in the adulation that le tout Paris afforded to a successful writer. He acquired the nickname le bon David and, according to Horace Walpole, became ‘fashion itself’. Though the relationship was never consummated, he became intimate with the countess and grande dame Madame de Boufflers.

At that time, Jean-Jacques Rousseau was in big trouble following the publication of The Social Contract and Emile. Boufflers put Hume to rescuing Rousseau by sending him to the safety of England. In January 1766, at the end of his tenure at the embassy, Hume left for London with Rousseau. The two men had much in common, not least their infamy, and held each other in the highest regard. But Rousseau was prone to paranoia and began to suspect Hume of being at the centre of a plot to ridicule him. To protect his good reputation against Rousseau’s mighty pen, Hume reluctantly pre-empted Rousseau by publishing an account of the whole affair.

Final Years

In 1767, Hume took up his last appointment as Under-Secretary of State for the Northern Department (the predecessor of the Foreign Office). The following year, he retired to Edinburgh and built himself a house in St Andrew’s Square, where he lived with his sister Katherine.

Within ten years, shortly after the American Declaration of Independence (July 1776), Hume died from a ‘disorder of the bowels’. He wrote a concise autobiography, My Own Life, so near to his death that at the end he switches to the past tense:

I am, or rather was (for that is the style I must now use in speaking of myself, which emboldens me the more to speak my sentiments); I was, I say, a man of mild disposition, of command of temper, of an open, social, and cheerful humour, capable of attachment, but little susceptible of enmity, and of great moderation in all my passions. Even my love of literary fame, my ruling passion, never soured my temper, notwithstanding my frequent disappointments … I cannot say there is no vanity in making this funeral oration of myself, but I hope it is not a misplaced one; and this is a matter of fact which is easily cleared and ascertained.

In his eulogy, Adam Smith, who had recently published The Wealth of Nations (1776), wrote that his friend Hume approached ‘as nearly to the idea of a perfectly wise and virtuous man as perhaps the nature of human frailty will permit’.

The Newton of Human Affairs

Already at the age of eighteen, Hume complained about philosophy being engaged in ‘endless disputes’ of an entirely hypothetical nature. He disparagingly referred to rationalist systems such as those of Leibniz, Spinoza, and Descartes as ‘speculative metaphysics’. 

Newton, in contrast, set out only to describe and predict events, without seeking to explain them. One of his most famous phrases is, Hypotheses non fingo [I do not feign hypotheses].

I have not as yet been able to discover the reason for these properties of gravity from phenomena, and I do not feign hypotheses. For whatever is not deduced from the phenomena must be called a hypothesis; and mere hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy. In this philosophy particular propositions are inferred from the phenomena, and afterwards rendered general by induction.

Hume saw himself as extending Newton’s experimental method to the study of human nature and the ‘moral sciences’—whence the subtitle of A Treatise of Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects.

Empiricism and Skepticism

At the core of Hume’s radical empiricism are two tenets. First, there are no innate ideas: all knowledge and concepts must arise or else derive from sensory impressions. Without prior observation, Adam (from Adam and Eve) could not have inferred that fire would burn him, or water drown him. All that is not founded in sense experience is essentially meaningless. 

Second, all we can directly perceive are our internal mental states. The self is no more than a bundle or collection of various perceptions and sensations, ‘which succeed each other with an inconceivable rapidity’. Taken together, these two tenets have dramatically skeptical implications, undermining traditional concepts such as God, the soul, a persistent self, external objects, and causation.

The Problem of Causation

When it comes to causation, we never perceive a ‘necessary connection’ between events, only ever a ‘constant conjunction’ of one event following another, over and over again. The supposed causal link is missing from sense experience. Cause and effect are merely a habit of mind. But that the sun keeps on rising every morning need not mean that it will always rise every morning. Cause and effect, which underpins all science, is justified not by reason and deduction but only by induction (habit), which is unsafe.

Reason the Slave of the Passions

At the height of the Age of Reason, Hume was the great debaser of reason. ‘Reason’ he said, ‘is, and ought only to be the slave of the passions…’ 

Still today, most people think of choice and action as a battleground between reason and the ‘passions’ (desires, emotions, and sensations). Hume argued that it is in fact a battleground between the passions and the passions. For example, if I pass over dessert, this is because my desire to feel and look good is stronger than my desire to eat something heavenly. It can sometimes feel as if the passions are fighting with reason, when, really, it is an urgent passion, such as my desire for dessert, fighting with a calmer, longer term one, such as my desire for moderation which masquerades as reason.

Reason on its own cannot impel action. Its role is simply to supply us with true beliefs about the best means of achieving the ends that our passions have already determined. The aim of a monarch or general in delivering a battle exhortation is not to be right or logically sound, but to fire up the passions and try to make it so that the resolve of his men is greater than their fear.

A passion may be justified or unjustified, but cannot be true or false like a belief. When a passion is founded on a false belief, the problem is with the false belief rather than the passion. Once we have ascertained that there are no gremlins under the bed, or persuaded ourselves that there are no such things as ghosts, our fear of these things simply evaporates.

Morality and the ‘Is-Ought’ Problem

Because morality is about choices and actions, it cannot arise from reason. Or in Hume’s famous turn of phrase, ‘You cannot derive an ‘ought’ from an ‘is’.’ Prescriptive statements (‘oughts’) arise not from facts and reason but from values and feelings, especially the capacity for sympathy, which leads to pleasure in response to prosocial actions and aversion in response to antisocial ones. Whenever a prescriptive statement appears to derive from a descriptive one, this is only because there is a prescriptive premise that is missing but presumed. For example: ‘Stealing harms other people. Therefore, we ought not steal.’ The presumed prescriptive premise here is, ‘We ought not harm other people’—which is not a fact but a value judgement.

You can see why Immanuel Kant was disturbed by all of this. If Hume was right, science rested on habit rather than certainty, and morality on feeling rather than reason. His response, the 856-page Critique of Pure Reason (1781), emerged after a ‘silent decade’ during which he retreated into himself and published a total of just 23 pages. He later wrote that it was Hume who had awakened him from his ‘dogmatic slumber’.

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If you want to know what happened next, read The German Greeks, which tells the story of how Kant, Schopenhauer, Nietzsche, and others responded to the philosophical revolution that Hume helped to create.

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