Leibniz' lecture on the Greeks as the founders of rational theology – which was delivered by Leibniz himself at an ‘Academy’ in Vienna on July 1, 1714, and which is published here through the generous permission of the Leibniz-Archiv at the Niedersächsische Landesbibliothek in Hanover – is of course interesting as evidence of the breadth of his knowledge of the history of religious ideas. But from a philosophical point of view its main interest lies (1) in elaborating Leibniz' debt to Platonism – a debt which Leibniz made clear in his published letters to the French Platonist Remond but which receives reinforcement from this 1714 lecture; (2) in showing, more particularly, that Leibniz relied on Plato (and Aristotle) in developing a concept of ‘substance’ which would remedy the defects of ‘materialism’ and ‘mechanism’ and explain the immortality of the soul ‘naturally’, without recourse to ‘miracles’ or to ‘faith’ – a soul which could be a subject of divine justice in Leibniz' ‘universal jurisprudence’, and (3) in showing what Leibniz meant when he spoke of the ‘eternal verities’ being ‘in’ the mind of God but not caused by the mind of God.