The Reformed theology that dominated Cambridge in the mid seventeenth century tended strongly towards a voluntarist conception of God’s relation to morality, on which God’s will is the sole determiner of moral truths. This chapter demonstrates that over the same short period (c. 1642–51), the Cambridge Platonists all took a controversial stand against the voluntarism of their Calvinist colleagues, arguing for a kind of moral realism on which God’s goodness precedes, and in a sense even constrains his will. They did this despite the fact that their realist position was routinely denied and condemned in Reformed preaching about predestination. Whichcote, More, Cudworth and Smith’s arguments against voluntarism and in favour of realism in this narrow time period suggest close intellectual contact while also matching Tuckney’s description of the doctrinal profile of Whichcote’s ‘learned and ingenious’ Plato-loving scholars.