This article considers the claim made by William Clifford that no belief should be held without sufficient reason and its implications for belief in God and public theology. Responses to Clifford, notably by William James, have tended to emphasize the personal side of religious belief. Public theology assumes a means for settling disputes through rational argument. However, David Hume and Immanuel Kant raised significant challenges to belief in God, and this developed during the nineteenth century into a rejection of public theology. This article traces the intellectual history behind Clifford's claim, and argues that, by the time that Freud offers his claim that belief in God is immature, the justification for public theology has been undermined. By clearly identifying the challenge facing public theology, this article lays the framework for constructing a response to the critique of reason given by Kant and the scepticism of Hume. If public theology is to be defended, this response is both necessary and timely.