The Lord did not say, “I am custom”, but “I am Truth”.’ So, allegedly, Pope Gregory VII, in words that – among medievalists at least – have become almost as well known as the Scriptural text to which they refer, ‘I am the way, the truth, and the life’ (John 14.6). The Gregorian dictum embodies the paradox at the centre of the movement for Church Reform in the eleventh century, a paradox which continues to shape historiographical discussion of the period. On the one hand, Gregory and his circle presented themselves as uncompromising fighters for the truth of their vision of the Church, prepared to dismiss any appeal to established practice, however venerable; on the other, and in the same moment, however, they themselves appealed explicitly to past precedent in broadcasting their manifesto. In the comment attributed to Gregory, the authority of ‘the blessed Cyprian’ (mediated in turn by Augustine) is invoked to sanction the rejection of custom. To ‘custom’, then, the reformers opposed not ‘truth’ as a timeless absolute, but a notion of truth embedded in a tradition of moral language. Like many revolutionaries, they saw themselves as restoring their society to a pristine state from which it had fallen away – deaf to the accusation of their opponents that such ‘reform’ was in fact irreparably destructive of the peace of the community. In part because eleventh-century questions about the moral, and in particular the sexual, behaviour of the priesthood continue to be relevant in modern churches, modern scholars continue to take sides over Reform, depicting Gregory VII either as faithful restorer or as demonic innovator. This interpretative deadlock suggests, perhaps, that we should look again at the reformers’ paradoxical notion of truth as it emerges through their use of inherited language. My suggestion is that crucial to the truth of Reform in the eleventh century was its reassertion of a very ancient rhetoric of gender.