The focus of this volume is on ‘heterodoxy’, specifically on how positions divergent from orthodox doctrine in both science and religion in the early modern period might be related. While within the classical traditions of knowledge there was a standard topos, ‘paradox’, to denote departure from established positions, a ‘heterodox’ position in theology was, as Ian Maclean explains in the introduction, one step away from heresy, a contumacious persistence in error. A concentration on heterodoxy is a way to gauge historically how deviation in the field of science might be correlated with deviation in the field of religious belief, or vice versa. More importantly, it is an attempt to discuss how past thinkers situated their own beliefs and knowledge in relation to the received standards of knowledge of the time.

The essays in the volume engage with this theme in a variety of ways. Some thinkers were vocal about their views, others less so. Thus Giulio Cesare Vanini, executed in 1619 for atheism, blasphemy and impiety, had published (in De admirandis and Amphitheatrum) his views, albeit in a somewhat garbled way. Nicholas Davidson carefully decodes these publications to show that Vanini believed that there was no spiritual world beyond the natural, and that therefore the traditional arguments for the immortality of soul and providence were a sham, and that eternity of matter and transmutation could explain the origins of life. In contrast, John Donne led a life that successfully and outwardly conformed to the established Church, but David Wootton has uncovered Donne's sustained sympathy with the Familist religion of love. Other, more obviously ‘heterodox’, thinkers turn out to be less unorthodox than one might expect. Hence Margaret Osler argues against the portrayal of Gassendi as a ‘libertine’, given his concerns with providence, finality and immortality of the soul in his natural philosophy. William Carroll also offers a revisionist account of how Galileo's conceptions of science and biblical exegesis had much in common with orthodox positions, notably with the Aristotelian, demonstrative science of causes and the exegetical positions of Counter-Reformation Catholicism.

Then there were those figures whose scientific and religious concerns were inextricably fused. Stephen Snobelen maps out Isaac Newton's dual reformation of natural philosophy and of religion, guided by the prisca tradition. Newton's God of dominion and his conception of nature as contingent on the existence of God were two halves of a whole. David Boyd Haycock argues that William Stukeley, inspired by Newton and his followers' works (especially Whiston) to combat atheism through natural philosophy, sought to prove the truth of the Trinity through archaeology, which Stukeley believed to be a ‘science’. Joseph Priestley, in John Brooke's reading, is shown to be a radical in both scientific and religious matters, concerned with the purification of religion and gases, rather than a dissenter with a dogmatic adherence to the orthodox position of phlogiston. These links between scientific and religious heterodoxies should not, however, be taken as proof that specific theological positions imply and compel adherence to specific views of nature or cosmos. As Tabbita von Nouhuys shows in her case study of a Remonstrant (Philip van Lansbergen), a Calvinist (Gisbertus Voetius), a Catholic (Godefridus Wendelinus) and a Jansenist (Libertus Fromondus), the acceptance or rejection of Copernican heliocentrism did not fall along confessional lines. In a similar vein, Scott Mandelbrote's study of Nicolas Fatio de Duillier shows that problems such as the failure to develop his notions sufficiently for the likes of Newton or to develop a respectable, orthodox career were important factors in the marginalization of his own ideas about God and gravity.

There are also examples of those who clearly drew a line between faith and nature. Ian Maclean shows how Pomponazzi, Gratarolo and Cardano, among others, were quite aware of the theological implications of their medical or natural-philosophical views, but treated them as belonging to different disciplinary domains. Cees Leijenhorst argues similarly that Thomas Hobbes insisted on an epistemological separation of faith and reason. Yet philosophically, given that one could state that God exists, and one knew that everything that exists is a body, Hobbes could define God as infinite, corporeal spirit – the subtlest fluid. This view was neither inconsistent nor ad hoc nor atheistic, though Hobbes did fall short of explaining in his natural philosophy the location of such a divine fluid. Nevertheless, there was perhaps a sense in which the confessionalization of physics – the spatial separation between Christ and the host (the Eucharist) and the temporal separation between God's intention and historical events (predestination) – had reached a stalemate by the end of the sixteenth century, as Christoph Lüthy suggests. Mersenne's solution was to develop a republic of letters, a new type of community, in which the establishment of observational and experimental facts formed the basis of interconfessional dialogue. This was not a secularization of nature, though, since for Mersenne the point was to focus on the phenomena of God's creation rather than causes, in the way advocated by other newly emerging scientific societies.

This is a rich collection of case studies which should provide much food for thought for those scholars interested in the topic of ‘science and religion’, not least because the essays, collectively, militate against any simplistic generalization about the relationship between the two spheres. Orthodoxy and heterodoxy are correlative terms in that one is defined by the other, though perhaps ‘heterodox’ is more often a term of criticism and abuse, rather than a badge to be worn with pride. Those whom we historians regard as heterodox in their scientific and/or religious views frequently believed that theirs was the right and true view and that theirs was the position that should be orthodox.