Publication of An essay on spirit in 1750 was, on the face of it, no particular landmark in the history of heterodoxy. There had been arguments in Anglican circles since the 1680s about ‘mystery’ and the Holy Trinity, all part of the assault on fundamental articles of belief waged by such critics as John Toland and Anthony Collins after the Revolution Settlement, a time when interest in Arian ideas was reviving among Isaac Newton's followers, particularly Samuel Clarke and William Whiston. An essay on spirit – this latest expression of a highly developed Arianism – was couched in scholastic, even esoteric language, of apparent interest only to controversialists on either side of the question. What, however, made it a cause célèbre was the talk from the moment it left the press that its author and apologist for what we have recently been reminded was the archetypal Christian deviation was none other than one of the most senior members of the Church of Ireland – the bishop of Clogher, Robert Clayton, himself an Englishman by birth. Though not every commentator could or would believe this ascription, the bishop himself never attempted to deny it and, before long, the unsettling evidence of the extent to which heresy had penetrated the highest circles of the Anglican establishment was beyond serious doubt. Its appearance (and the writings which followed) led to vigorous counter-blasts on both sides of the Irish Sea from a range of clerical and lay opinion that extended well beyond the confines of any church ‘party’. Having spent the previous half century countering, with some success, the different strains of deism and free-thinking on the frontiers of Anglicanism, a broad band of clergy was alarmed that Clayton's writings of the 1750s bore disturbing witness to the presence of traitors within the citadel who, in challenging the Church to tolerate their continued presence, were ready to endanger its moderate latitudinarian character. Moreover, An essay on spirit appeared at a time when the writings of Middleton and Hume also demanded the notice of theologians, and the ‘Church in Danger!’ had not ceased to be an appropriate battle cry to marginalised Tories.