A Discourse Concerning the Unchangeable Obligations of Natural Religion

Clarke's 1705 Boyle Lectures — natural-law ethics and the rational foundations of moral obligation

Tradition: Newtonian natural theology / English rationalism / natural-law ethics

Clarke's 1705 Boyle Lectures — the eternal and necessary fitness of things as the rational ground of moral obligation

Delivered as the second-series Boyle Lectures for 1705 at St Paul's Cathedral (Clarke had given the first series in 1704; the second series followed immediately the next year) and published in 1706 as the companion to the 1705 'Demonstration of the Being and Attributes of God', 'A Discourse Concerning the Unchangeable Obligations of Natural Religion, and the Truth and Certainty of the Christian Revelation' applies the rationalist demonstrative method to natural-law ethics and Christian apologetics. The book is structured in two main parts. Part I: 'Concerning the Obligations of Natural Religion' — the philosophical case that morality is grounded in eternal-and-necessary 'fitnesses or unfitnesses of things' that reason discerns. Clarke's central thesis: there are 'eternal and necessary differences in things' (some things are objectively right or fitting, others objectively wrong or unfitting, independent of any agent's will or convention); reason recognises these fitnesses; the recognition imposes moral obligation; God himself acts according to these eternal fitnesses (rather than constituting them by divine will, as the voluntarist tradition had held). The position is intellectualist moral rationalism in its strongest eighteenth-century form. Part II: 'Concerning the Truth and Certainty of the Christian Revelation' — the apologetic case that Christianity is the revelation that completes natural religion. Clarke argues that natural religion alone, while rationally sufficient to establish basic moral obligation, is insufficient for human moral need (because humans are weak, prone to error, and have inadequate motivation for moral practice); the Christian revelation supplies what natural religion lacks (specific moral instruction, motivating divine example, eschatological sanctions). The book is the canonical statement of eighteenth-century English ethical rationalism; it provoked Hume's attacks on rationalist ethics in the second Enquiry (1751) and was a major reference point for the broader rationalist-sentimentalist debate (Cudworth, Clarke, Wollaston on one side; Hutcheson, Hume, Adam Smith on the other).