Despite choosing a title that deliberately echoes Jonathan Israel's Radical Enlightenment: Philosophy and the Making of Modernity, 1650–1750 (2002), Stéphane Haffemayer contends that the notion of a “radical Enlightenment” should not be restricted to the impact of Spinoza's philosophy on late seventeenth- and early eighteenth-century intellectual life. It can also legitimately be applied to the projects of improvement devised by Samuel Hartlib's network, which relied on reason and experimentation to reform seventeenth-century English society. Haffemayer's argument is supported by an impressively detailed analysis of the complete Hartlib Papers, available online thanks to Mark Greengrass (who wrote the preface to the book), Michael Leslie, and Michael Hannon. After George Turnbull's and Charles Webster's major works on Samuel Hartlib, no extensive study of the Hartlib Circle had been produced, despite the publication of the electronic edition in 2013. Moreover, Haffemayer's book fills a gap in French scholarship on the intellectual context of the English Revolution.

The four parts of the book follow a chronological order, starting with the ideological foundations of Hartlib's reformation projects. From his arrival in England in the 1620s, the Protestant refugee who had fled the perils of the Thirty Years War in north-central Europe unfailingly acted in favor of religious peace and the union of Protestant churches. He first joined the Puritan milieu in Cambridge, where he also came across Francis Bacon's works, which later served as a model for his own projects, especially his pedagogical reform. But the advancement of learning was also perceived by Hartlib and his friends as one of the key elements that would bring about the Millennium. The second part describes Hartlib's role as an intelligencer in the decade prior to the Civil Wars, when he actively promoted the projects of the Scottish irenicist John Dury, who spared no effort to achieve the reconciliation of Protestant churches. Hartlib sought intellectual and financial support from Puritans and anti-Arminians; he wrote about the “Protestant Cause,” edited numerous texts, and acted as mediator between Dury and influential men, such as the ambassador Thomas Roe. Hartlib's “parallel diplomacy” (121; here and throughout, my translations from the French) aimed to ensure the support of an English party for the Palatinate, when the Stuart kings refused to intervene in favor of European Protestants in the context of the Thirty Years’ War. Hartlib received news, mostly from Holland and Germany, which he copied and sent to his English correspondents, such as John Pym and Cheney Culpeper. This diplomatic function required discretion, especially as Hartlib, a refugee with links to Puritanism, was being watched. In the third part, Haffemayer shows that Hartlib continued to act as an intelligencer, in the service of Parliament, during the Civil Wars. At a time when the number of printed texts—books, broadsides, and periodicals—multiplied, and contradictory information was circulated, Hartlib carefully checked the facts before he copied extracts from those texts, and transferred them to the parliamentary side. His role as “political correspondent” (307) was recognized in 1645, when he was granted financial support by Parliament. In the fourth part, Hartlib's “enlightened radicalism” (377), or his determination to transform society by reconciling reason and faith, is the focus. Hartlib understood Charles I's death as a providential condemnation of papism, while the end of episcopalianism should lead to the liberation of consciences and the rule of reason. The Interregnum was indeed perceived by Hartlib and his friends as the moment when the complete reformation of society could be realised. It first seemed that Oliver Cromwell would foster the projects of the Hartlib Circle, in particular the union of Protestant countries under English leadership, the restoration of moral order at home, and the promotion of education. The return of the Jews also gave Hartlib and his friends hope for their conversion and the subsequent coming of the Millennium. Haffemayer's analysis of Hartlib's and Cromwell's relationship draws an unusual portrait of the Lord Protector as a man who did not rule entirely on his own, but who sought advice from unofficial counsellors. Hartlib remained a “conduit-pipe” (422) throughout the 1650s, circulating news about the persecutions of Protestants, such as the massacre of the Waldensians in 1655. Haffemayer gives a long and detailed presentation of the iconography published on the subject at the time (454–70), just as he does in the second part of the book, on the 1641 Irish Rebellion (247–83), drawing a parallel between the two events and the way they were received by the Hartlib Circle. Although the link with Hartlib himself grows thinner in these pages, Haffemayer excels at analyzing this iconography, as he has already shown in previous publications, for example Images et révoltes dans le livre et l'estampe (2016). Finally, Hartlib's interest in science and experimentation is dealt with at the end of the fourth part of the book. One might wish that an entire part had been devoted to the subject. As Haffemayer himself admits several times (for example, at 470 and 484), this aspect of Hartlib's correspondence deserved more discussion. The Hartlib Circle's interest in the improvement of agriculture, and the exploitation of saltpeter, for example, is here studied, as are their projects for Virginia and Ireland, where they hoped to establish ideal Christian societies. None of these projects was realized, and Haffemayer concludes on the intellectuals’ “disenchantment” at the end of the Protectorate (523).

More than an intellectual biography of Samuel Hartlib, Haffemayer's book is an essential contribution to the study of “political culture” (22) and its formation in the context of the English Revolution. The detailed and learned analysis of the Hartlib Papers presented here reveals the pivotal role of intelligence and communication in the unfolding of events between the 1630s and 1650s. Accordingly, Haffemayer does not merely draw “the background of the English Revolution” (58), for he convincingly shows the actual and effective participation of Hartlib and his network to the religious and political events of the mid-seventeenth century.