These two books together serve to introduce Dirck Volckertsz Coornhert (1522–90), a writer who features only in the most inclusive version of the canon, to an international readership. Coornhert's principal claim to fame is that his Zedekunst (1586), the work which is translated as Ethics in the second of the books under review, was the first comprehensive ethical treatise written in a European vernacular. Part of his obscurity is, indeed, due to his having written chiefly in Dutch, a language as cosmopolitan in his own times as it is inaccessible to most readers today. Alongside Gerrit Voogt's edition and translation, we now also have an English-language monograph on Coornhert based on Ruben Buys's doctoral thesis, which won the Netherlands’ top research prize in the humanities and social sciences in 2010. Together they make a powerful case that Coornhert and the tradition that he represents deserve to be better known.

Buys's project is two-fold. He expounds Coornhert's ethical philosophy, tracing its sources in classical antiquity, in the Dutch vernacular tradition of the late Middle Ages and in the spiritualism of the Radical Reformation. And he places Coornhert at the centre of a web of like-minded thinkers in his own time and in subsequent generations. Only at the end does it become clear that he is suggesting nothing less than a new intellectual genealogy for Spinoza and the Radical Enlightenment.

Calvin called Coornhert a beste sauvage and his teachings ‘diabolical blasphemy’. You can understand why orthodox Protestants might be shocked by a man who wrote a book entitled That eradicating evil is easy. Coornhert taught an ethics of perfectibility. In his view evil consisted, not of deprivation as Augustine might have argued, but more straightforwardly of ignorance. By ‘original sin’ he simply meant the ignorance in which we are all born: or, as Buys puts it, ‘a kind of socio-cultural blemish of prejudice and delusion, a bath of misapprehension into which everyone is dipped at birth’ (p. 115). Humanity's means of shaking off that legacy is ‘the unextinguished spark of divine reason within us’ (p. 47). The divine origins of this reason mean that it is ultimately an act of grace, but he compared it to the talents in the parable: the gift is given to all, and it is absolutely up to each individual to make of it what he or she will. Coornhert was scathing about strong doctrines of depravity, which he saw as lazy excuses for moral laxity.

So it is no surprise that Arminians were said to draw their inspiration from Coornhert ‘as a babe sucks all he needs from the breast’ (Buys, p. 229). But this went beyond asserting free will. If it is through reason – divine in origin or otherwise – that we are able to perceive and embrace righteousness, then the role both of the Church and of Christ is open to question. Buys claims that Coornhert relegated biblical revelation to an optional supporting role in the drama of salvation. He deliberately wrote his Zedekunst without citing Scripture at all, supposedly having been challenged by one of his disciples to make his argument by using reason alone, unsupported by authority. Buys perhaps pushes this point too far: most Protestants accepted that Bible-reading was desirable rather than essential for individual salvation. Coornhert's logic might have implied that virtuous pagans could be saved simply by the law of nature which divine reason revealed to them, but what he actually said was that that law ‘enabled them to acquire the knowledge of Christ that leads to salvation’, despite not knowing Christ's name (Buys, p. 207). Still, there is no doubt that this emphasis on reason led Coornhert to a radical inwardness in which forms and sacraments of any kind were dispensable optional aids. It made him praise doubt: ‘not just a useful prerequisite for certain knowledge: it is also the root cause of the desire to acquire the necessary knowledge’ (Coornhert, p. 177). Since doubt constitutes becoming aware of your own ignorance, it was for him almost a form of repentance. By contrast, faith as such hardly registered in his ethics, knowledge having taken its place. Naturally, therefore, he was also absolutely insistent on freedom of conscience, for reason could not perform its saving work in a straitjacket. He claimed that his first motive for writing was to oppose religious compulsion.

Coornhert's work is worth attention in its own right, and Voogt's sensitively translated and interpreted edition is going to be of enduring value. Buys's achievement, however, is to contextualise these doctrines. He tracks a prehistory of this rationalism in a series of Dutch vernacular texts from the thirteenth century onwards, a tradition which was turbocharged by fifteenth-century humanism's return to the classics. In the later sixteenth-century Netherlands, Coornhert was the most articulate but by no means the only advocate of these doctrines, and Buys wants to describe a loose movement of ‘Good-Thinkers’ who advocate – it is an oddly opaque phrase – ‘vernacular rationalism’. We come relatively late in the day to the most important link in this chain: Erasmus, whom Coornhert called Europe's true phoenix, in whom the ancient world was reborn. Buys is quick to insist that Coornhert and his generation had genuinely added something to Erasmian moralism, and plainly they had, but the similarities are more striking than the differences. Coornhert certainly rushed in to several positions where Erasmus had feared to tread, and was emboldened by reading Sebastian Franck and other Spiritualist writers as well as simply by the times he lived in. But he vigorously rejected the Spiritualists’ mystical anti-intellectualism. Erasmus’ view that true happiness consists in a quiet conscience, that rational self-interest therefore pursues virtue, and that therefore ‘there are no people more Epicurean than godly Christians’, is a fair summary of the doctrine which Coornhert would go on to espouse.

Buys does enough to establish that this ethical rationalism had a decent foothold in the Dutch intellectual world of the Reformation age, but this is not a work of cultural history and he does not try to track its wider social influence. He focuses on its legacy instead. The most striking section of the book focuses on Spinoza's translator and associate Pieter Balling, and especially on his The light on the candlestick (1662), ‘the first “Spinozan” text ever to be published’. Virtually all of the supposedly striking novelties of that text, he argues, were anticipated, often explicitly, in Coornhert's work a lifetime earlier.

This might be taken to mean that Coornhert was, to use the seventeenth century's favourite insult, an atheist: but Buys wants to turn that argument around. Coornhert's theology was unorthodox, but theology it was, and although he came close to deifying reason, he was unambiguous in asserting divine transcendence: no Spinozan pantheism. This book's ultimate argument, then – contra Jonathan Israel and other prophets of radical-Enlightenment secularism – is that the radical Enlightenment arose from a ‘religious orientation’, and that ‘the radicalisation of thought in the Dutch Republic during the 1660s and 1670s was, to a great extent … a religious and spiritual quest’ (p. 246). Or, as he might have said: modernity is all just footnotes to Erasmus.