Scepticism undergoes a revival in sixteenth-century Europe, with Michel de Montaigne (1533–92) being instrumental in fostering renewed interest in the Pyrrhonian tradition (particularly in his essay ‘An Apology for Raymond Sebond’ (1780)). It is Pyrrhonism, as Popkin notes, that ‘became central in the intellectual battles of the late sixteenth century’. Popkin speaks of a crise pyrrhoniene in the period, with scepticism being brought to bear on theology in the wake of the Reformation and the fierce doctrinal conflicts that flared up between Protestants and Catholics. Authority is a key issue in this context, with both sides claiming to be the sole authority for the Christian faith, and freely accusing each other of scepticism with regard to the fundamentals of belief. This was a damning indictment in that culture: in the ringing words of Martin Luther (1483–1546), ‘[t]he Holy Ghost is not a Sceptic’, so no true Christian could be either. Pyrrhonism is even mocked in the work of Rabelais (?1494–1553), through the figure of the philosopher Wordspinner in Gargantua and Pantagruel (1532, 1534). Wordspinner’s intellectual evasiveness leaves both Panurge and Gargantua bemused and exasperated; the latter declaring of his convoluted arguments that, ‘[i]t will be easier to seize lions by the mane . . . than to catch philosophers of this kind by the words they speak’.

It is Descartes (1596–1650), however, who is generally considered to be the figure who brings scepticism most fully into the modern philosophical world, in his quest to find a secure basis for a theory of knowledge. He subjected all his beliefs to scrutiny, seeking to locate that elusive starting point from which he could then build outwards with assurance. This proved to be the famous proposition, cogito ergo sum, ‘I think therefore I am.’ The one thing that Descartes could never doubt was that he was thinking, even if the truth of the content of his thoughts posed more problems for him. Once he started investigating these thoughts, however, they soon provided more reinforcement for his new system.

Descartes is generally regarded now as only a quasi-sceptic, since although he describes himself in the Third Meditation as ‘a being that doubts’ he proves only too ready to embrace proofs for the existence of God. Indeed, he regarded himself as the enemy of the new Pyrrhonism in French thought, considering this to be a particularly dangerous trend which needed to be countered if Christian belief was to prevail. Descartes’ brand of scepticism was designed to overcome scepticism: ‘strategic’, in one commentator’s assessment. On the subject of God Descartes’ philosophical radicalism slips. Once that proof is in place, based on principles such as that he has an idea in his mind of a perfect being against which his own imperfection can be measured, Descartes moves rapidly to build-up a series of propositions in which he can believe with complete confidence. In sceptical terms of reference, the existence of God is never really placed in question, which makes Descartes’ project of formulating a theory and system of knowledge considerably easier. As Bernard Williams has observed, The road that Descartes constructed back from the extreme point of the Doubt, and from the world merely of first-personal mental existence which he hoped to have established in the cogito, essentially goes over a religious bridge. Taking his concern to be the foundations of scientific knowledge, these are provided by God; taking it to be the foundations of the possibility of knowledge, these too, and in a more intimate sense, are to be found in God.

The belief undermines the scepticism, in other words, whereas for the true sceptic it would be the other way around: faith would be out of bounds as a basis for proof, yet another unsubstantiated assumption looking around in vain for a criterion to justify it.

Ultimately, Descartes is not really a philosopher who leaves one feeling too ‘uncomfortable’, although he does succeed in establishing scepticism as a key element in modern philosophical discourse. As one commentator has put it, the irony of Descartes’ researches is that ‘[h]is “refutation” of scepticism left it in better shape than before’. Negatively oriented though it may be, scepticism is nevertheless now firmly a part of the philosophical mainstream.