This is the second part of Martin Mulsow's influential study Radikale Frühaufklärung in Deutschland, 1680–1720 (Göttingen 2018) in an English translation by H. C. Erik Midelfort. Following on from Enlightenment underground: radical Germany, 1680–1720 (Charlottesville, Va 2015), Mulsow continues his exploration of heterodox ideas and their circulation in the German lands around the turn of the eighteenth century, challenging and revising the long-established view of the German Enlightenment as a fundamentally moderate and cautious affair.

The book's seven chapters are devoted to various scholarly discourses about the mortality of the soul, idolatry, atheism, natural law, Socinianism and the humanity of Moses and Jesus as founders of religion which frequently transgressed the boundaries of what could be said with impunity at the time, yet rarely had serious consequences for their proponents who developed their own strategies for avoiding the authorities. Among those strategies were the circulation of texts in manuscript or clandestine publications which could not be traced back to their sources because they appeared anonymously, were published abroad – mostly in the Netherlands – under false imprints or without any imprint at all. Others might involve presenting dangerous teachings in the form of ‘paradoxes’ which juxtaposed opposing doctrines, leaving the reader or listener to derive their own conclusions or to ‘exercise a learned ignorance’ or ‘docta ignorantia’ (pp. 258–9)

Each chapter follows the ideas to the environments from which they arose and in which they were discussed, leading the reader to the Protestant university towns of central Germany, such as Halle, Jena, Helmstedt and Leipzig, to Frankfurt on the Oder, and to the eastern periphery of the country, where the control of the authorities could barely reach. As Mulsow emphasises, the bigger picture he draws thus goes beyond Halle as the centre of the German Enlightenment with Christian Thomasius as its protagonist, to include ‘a multitude of less well-known thinkers from various and unexpected locations in Germany’ (p. 328), while also showing the ‘Europe-wide entanglements’ (p. 338) of these scholars.

As in Enlightenment underground, Mulsow applies a method he calls ‘philosophical microhistory’, which ‘requires following even the smallest clues in an effort to perceive a social context that has not hitherto been studied by historians’ (p. 13). This might involve ‘studies of the circulation of ideas that follow the spread of clandestine manuscripts’ (p. 13) which were copied, changed and shared for a variety of purposes. He complements his study of printed sources with the examination of a broad range of letters, diaries, travel journals and legal documents, all closely scrutinised to establish new connections between different historical actors and their works.

Mulsow's book thus offers deep insights into the kinds of ideas circulating among scholarly elites in Germany in the early Enlightenment as well as into the different means of their circulation. It is in the nature of the material that many texts cannot be clearly ascribed to an author, that publishers and places of publication are false or concealed, and that individuals can no longer be traced. Hence, many of Mulsow's conclusions about the trajectory of texts and ideas are ‘pure speculation’ (p. 323), as he openly concedes, and rely on the relative likeliness of X having known Y and meeting Z – a history of how things might have been and how they could have happened. Rather than attempting to offer definitive answers, Mulsow's book thus gives a good idea of the broader environment in which scholarship took place and radical ideas could form, while opening up many different avenues for further study.

Midelfort's translation offers a slimmed-down version of Mulsow's original German text, omitting a chapter on the reception of Jakob Böhme, which is to appear as a separate book, and reducing the volume of the scholarly apparatus by deleting most of the quotations from the footnotes. Primary source quotations from German or Latin are given only in English. These cuts arguably de-clutter the text, but at the same time also make it harder for readers to follow Mulsow's train of thought or see if they would have agreed with the author's or translator's interpretation of any given text, which is regrettable given that most of Mulsow's sources are not easily accessible elsewhere. But more advanced readers can always turn to the German version.

Given Mulsow's focus on lesser known thinkers of the Enlightenment it would have been welcome if he had extended his forensic approach to explore the role of learned women – beyond the occasional reference to Queen Sophie Charlotte of Prussia as the audience for some of the heterodox works he discusses. It would also have been interesting to learn something – however little – about the wives, mothers and sisters of the learned men of the universities and the extent to which they might have shared their husbands’, sons’ and brothers’ concerns with the tensions between reason and religion. Maybe there is a book yet to be written.

In the meantime, it is important to bring Mulsow's influential work to the attention of English-speaking audiences as it marks a significant shift in the historiography of the early Enlightenment and the place of Germany within it. In particular, it uncovers the depths of a radical German Enlightenment largely hidden from the view of those relying on printed material only. Besides, it establishes important connections between English and continental debates more generally and highlights once again the role of the Netherlands as a publishing hub in this context. It has interesting things to say, for instance, about the reception and impact of the works of Thomas Hobbes and John Locke in Germany, or about the role played by John Toland as a go-between connecting people and aiding the transmission of texts and ideas. Finally, it sheds new light on the ways in which debates about the immortality of the soul, the conflicts between reason and religion and the progress of natural law crossed linguistic and cultural borders in early modern Europe as scholars engaged with each other's works.