Valla first exposed as a fraud the Donation of Constantine, the document purporting to express the gift of the western empire to Pope Sylvester by the emperor Constantine, and thereby incidentally proving the sovereignty of the Pope over secular governments. One of his influential treatises was De Voluptate (‘On Pleasure’, 1431), playing off the systems of the Stoics, the Epicureans, and Christian ethics. De Libero Arbitrio (‘On Free Choice’, 1435–9) takes issue with Boethius’s treatment of free will, arguing that God’s foreknowledge is compatible with human free will, but that his power is not. Valla was also an acute early critic of the multiplicity of scholastic categories and distinctions, and one of the first writers to see that existence is not a kind of predicate.