The people who were most influential in Descartes' early life were all women. His mother died when he was one year old. That might have provided a context in which he could have formed close family ties with his two siblings, Pierre and Jeanne, or with his father, Joachim. Apart from Jeanne, however, he seems to have been estranged from his immediate family and to have directed his affections from infancy toward others. The first person with whom he bonded closely was his nurse, with whom he maintained a residual emotional link for the rest of his life. According to his niece, Catherine, Descartes specifically asked as he was dying that those who managed his estate ‘take care of the living expenses of his nurse, whom he had always cared for when he was alive’. This final token of gratitude should not be exaggerated. It probably indicates a redirected love for his mother rather than a deep, authentic love for someone whom he had not seen for more than fifty years. The other people most closely involved in Descartes' early life were his grandmothers. Since his father, Joachim, worked in Rennes for part of each year from 1596 to 1600 – when he remarried and moved permanently in Brittany – Descartes was effectively cared for until he went to college by his two grandmothers, Jeanne Sain and Claude Ferrand.

According to his own account, Descartes had gone ‘to war’ with the French Jesuits in 1640. While that controversy was still active, he opened hostilities on a second front two years later with the rector of Utrecht University, Gisbertus Voetius (1589–1676) and, eventually, with the Utrecht city council. At the height of this controversy, Regius was described in a student's Latin rhyme as the ‘French liar's monkey’. The ‘French liar’ himself, Descartes, was characterized by a somewhat reluctant critic as follows: ‘The man lacks all modesty, is proud, supercilious, scandalous and quarrelsome.’ The unusually sharp language used by both sides, even when judged by the standards that prevailed at that time, shows the depth of the rift involved.

As usual, Descartes offered a benign and self-serving interpretation of his motivation. ‘All I ask for is peace … but I see that, to obtain it, I have to wage war a little.’ It is hardly credible however that, while living in comparative solitude in a rented castle at Endegeest (in the province of Holland), he had to engage in public controversy with influential Dutch theologians in another province (Utrecht) in order to protect his tranquillity. It is much more likely that he blundered into this theological and political minefield by making careless comments about Voetius in an appendix to the second edition of the Meditations, which was published in Amsterdam.

Bread and wine, and the seasonal changes that affect their production, were among the most familiar features of life in the Loire valley, in central France, in the sixteenth century. The appearance of the ‘plague’, although an infrequent event, was much more prominent in public consciousness. None of these realities was well understood. The range of grapes cultivated in this region was very extensive, and the wines produced were equally diverse. Growing grapes and producing wine relied on traditional techniques that had been passed on for generations. Those involved in viticulture could easily recognize a good season, with the right combination of spring rain and intense heat in midsummer, and they succeeded admirably without a scientific oenology. Likewise, the production of bread and other familiar foods did not presuppose biochemistry and any of its cognate sciences.

The plague, however, was a different story. In one province alone, in 1631, it killed 40,000 people. No one understood what it was, how it arrived in a town, or why it eventually abated, although they noticed that it tended to vary in intensity with the seasons, being worst in summer. They also knew that it was likely to cause a very large number of painful deaths and that the best defence was to flee, preferably before the plague arrived in a town.

Descartes' correspondence during the two years prior to publishing the Principles is almost silent about the wider political and military turmoil within which he conducted his own intellectual war. Charles I had been king of England since 1625. He was formally challenged by Parliament in June 1642, in a document called the ‘Nineteen Propositions’, because of the arrogance and arbitrariness with which he allegedly exercised his royal powers. His formal reply, 18 June 1642, did little to satisfy his critics. The civil war that resulted brought Cromwell to power and, in January 1649, led to the public execution of the king by order of Parliament. During these tumultuous years, a number of royalist intellectuals emigrated to France and subsequently became correspondents with Descartes and, in some cases, supporters of his philosophy. They included Kenelm Digby and the two Cavendish brothers, William (marquis of Newcastle) and Charles.

The situation in the United Provinces was politically more stable than in England but, militarily, was just as unpredictable. The Stadtholder was constantly under pressure, both at home and on the battlefield, because he failed to synchronize military successes with political support, especially in the largest and most economically powerful province, Holland, as he carried on an increasingly stalled campaign against the Spanish Netherlands in the south.

At the beginning of the year 1640, Descartes was still living in Santpoort. He had given up the idea of publishing a selection of objections and replies to the Essays, and had been working instead for some weeks on what he described as ‘An Essay on Metaphysics’. Although this was not his first incursion into metaphysics, it represented a significant departure from what he had been doing during the previous decade and a return to a project that had been deferred since 1629. In that year he had written to Father Gibieuf, a theologian and member of the Oratory in Paris, that he would hold him to his promise to correct ‘a little treatise’ that he hoped to complete within two or three years. Descartes had evidently intended to contribute to the anti-libertine literature, in which the names of Mersenne and Garasse were so prominent, and to write about atheism and the human soul. The following year, 1630, he told Mersenne that he had worked on almost nothing apart from metaphysics for nine months after arriving in the United Provinces – adding, on that occasion, that it would not be appropriate to publish anything about metaphysics until he first saw how his projected book on physics was received.

Since his ‘physics’ [i.e., The World] was never published, he had no indication from its success or otherwise of how his metaphysical speculations might be received when he returned to the project in 1639.

During the years immediately prior to his second departure for the United Provinces, Descartes struggled unsuccessfully with a number of fundamental problems in mathematics and philosophy. The results of those efforts are recorded in the Rules for Guiding the Mind in Searching for the Truth, which was published posthumously, and in comments made in the biographical paragraphs of the Discourse on Method. The intellectual milieu in which Descartes lived was as fluid as the uncertainty of the initial steps on his intellectual journey suggests. His foreign travels confirmed at least the narrowness of the education he had received from the Jesuits. They also exposed him to a wide range of disparate views – religious, magical, and mystical – that were defended by apparently genuine believers. Descartes seems never to have been enamoured sufficiently of anyone's thought to consider seriously adopting it. This same general scepticism applied more vigorously in the case of authors such as Campanella and Bruno. His glancing encounter with their work, however, provided the conditions in which Descartes briefly considered and definitively rejected all forms of magic and mysticism in favour of an ideal of mechanical explanation.

Descartes died in Sweden in 1650, a few weeks before his fifty-fourth birthday. He had spent most of his adult life in relative seclusion in what is now the Netherlands, while the Thirty Years' War waxed and waned around him. By 1667, when some French Cartesians arranged for the return of his remains to Paris, they had begun to publicize his works, to develop a characteristically Cartesian philosophy, and to be identified by critics as a ‘sect’. These early supporters included many philosophers who, apart from Nicolas Malebranche, are probably remembered today only as marginal figures in the history of Western thought. The name of Descartes, however, remains readily recognizable. He has entered the canon of Western philosophy so securely that that there is no longer any dispute about his significance.

Why was he important? Hardly for the phrase by which he is popularly remembered today, both by students of philosophy and by other readers: ‘I think, therefore I am’. This was not an original insight on his part, and it had a relatively minor role in his work. During the past century, Descartes has often been read as a metaphysician or, perhaps as frequently, as a philosopher who took seriously the arguments of sceptics. Alternatively, he is classified as a philosopher of subjectivity, as someone who outlined an internal map of the human mind and defended the irreducibility of conscious experiences.

Descartes made a decisive break with his past and a significant step toward his life's work – although this became clear only in retrospect – when he left France and travelled north to the United Provinces at the beginning of 1618. There is no evidence to suggest that he embarked on this journey with the intention of devoting his life to philosophy, or that he was considering emigrating permanently from France, as he did a decade later. His state of mind, in 1618, was that of a young man who was uncertain about a career. He had provisionally declined to follow his father and his brother into a legal career and had opted instead for the other standard path to social promotion in French life – as a gentleman army officer. He also seemed vaguely conscious of intellectual gaps in his education, and of the benefits of foreign travel to help remedy those deficiencies.

Descartes' formal education had been narrowly scholastic, and it had certainly not provided a basis for the fundamental reform of human knowledge that he eventually undertook. During this period of transition, the young Jesuit alumnus seems to have been willing to consider perspectives as disparate as the mystical and cabalistic writers of the Middle Ages and the astrologers and alchemists of the Renaissance. He mentioned authors as diverse as Ramon Lull, Johannes Kepler, and Thomas Campanella, and flirted briefly with the arcane philosophy of the Rosicrucians.

In late 1628, when he was thirty-two years old, Descartes set out for the United Provinces for the second time in his life. The reasons he offered friends for his departure from France were that he wished to avoid the customary distractions of a gentleman's life (such as visiting friends and attending court), and that he wanted to escape the heat of the French climate. Descartes' subsequent frequent changes of address, and his almost obsessive efforts to conceal his precise location even from trusted friends, make the first reason more plausible than it might otherwise seem. During the period from 1629 to 1633, the new immigrant had at least five addresses, at Franeker, Amsterdam (twice), Leiden, and Deventer, and on two occasions he considered leaving the country either to return to France or to visit England. Since he asked Mersenne not to reveal his address and seems even to have provided misleading return addresses on his letters, one must assume that he wished to enjoy the seclusion that he claimed was necessary for his studies. His quasi-eremitical success is reflected in the pun used by some of those who were frustrated by his hiding, when they spelled his name as ‘Monsieur d'Escartes’ (Mr. Evasion).

The two years immediately following his visit to France – 1645 and 1646 – were a transitional period in Descartes' life in many senses of that term. In Paris he had met a number of potentially supportive scholars, and he had begun almost immediately to cultivate their friendship. However, once returned to the north of Holland, he seemed to lapse into a general malaise. He heard on 25 November 1644 that his friend Bannius had died during his absence. During the following months he wrote relatively little; he tried with limited success to complete the missing parts of the Principles; and he completely sundered his friendship with one of his most loyal and committed followers, Regius. There was some compensation for this intellectual stagnation in the preparation of French translations of his two Latin books, the Meditations and the Principles, although the work involved in translating them was done by others. Midway through this period he also began to work on a completely new project – which he called the passions of the soul – partly at the request of Princess Elizabeth and partly in response to queries from Chanut. Even here, however, his tentative explorations were qualified by a lack of interest in publishing the results.

Those who were best equipped in the past to write a biography of Descartes embarked on the project with great reluctance and explicit apologies. This pattern was set by the first major biographer, Adrien Baillet, in the late seventeenth century. As he began the task, he had on his desk more original documents by Descartes and his contemporaries than anyone has ever collected since then. Nonetheless, he suggested that Chanut, Clerselier, or Legrand would have been a more suitable biographer than himself. Charles Adam was equally hesitant about writing his Life of Descartes (1910), even though he had just completed editing the eleven-volume edition of Descartes' works with Paul Tannery. ‘In the current state of our knowledge’, he wrote, ‘it will not be possible for a long time to complete such a work properly.’ Adam thought that a good biography would require preparatory studies of philosophical and scientific topics in the early seventeenth century, and more research on those who influenced Descartes and on his personal relations with contemporaries.

When the late Terry Moore asked me if I were interested in writing a biography of Descartes, I answered too quickly in the affirmative. I did not appreciate adequately the unsatisfactory state of Descartes' correspondence, although I believed that many of the studies that Adam talked about had been done during the past century.

The winter of 1646–47 was too cold for Descartes even to travel to The Hague. His last visit there had been toward the end of November 1646, and he deferred his next trip for another four months, until the end of March 1647. As in the previous winter, this reluctance of a formerly inveterate traveller was not due exclusively to the weather. He was also beginning to feel old and infirm, and his thoughts turned once more to considerations of mortality. Thus when Huygens mentioned the musical compositions of their late friend Bannius, Descartes told him that he did not value them highly, and then added: ‘If I die only of old age, I would still like some day to write about musical theory.’ At about the same time, he told Picot about changes in his daily routine. He had reduced his evening meal, he said, because his usual eating habits made him feel heavy and disturbed his night's sleep. That might have seemed trivial in other circumstances. Now, however, Descartes thought it was a warning sign of imminent ageing and a more reliable indicator of advancing years than his grey hair. Baillet noticed a number of related symptoms of Descartes' awareness of ageing.

During the years immediately following the condemnation of Galileo, Descartes held fast to his initial view that the cardinals had made a mistake, though one that was potentially dangerous for himself. His fundamental idea was that the decision involved a misunderstanding of the role of the Bible as a source of scientific knowledge. He also argued that he was not bound to accept the Roman decision as a matter of faith, and he hoped that it would be reversed in due course so that he could publish his World without fear of censure. He had to concede, however, that as long as there was no change of mind about Galileo by the church, the World would remain ‘out of season’ (i. 324). Descartes' refusal to publish The World was therefore not as definitive as it seemed to people like Mersenne, to whom he wrote: ‘If the reasons that prevent me from publishing it were to change, I could make a different decision without thereby being fickle’ (i. 367). We know now, in retrospect, that there was no change in Rome's censure, and that there was none either in Descartes' decision. His first book remained unpublished throughout his lifetime.

In these circumstances, the next-best option was to consider ways in which parts of his work that were not theologically sensitive could be released to the public.