  What is significant here is that – despite the radical changes in cosmology – this is is still an extremely medieval theory: causation is due to forms inhering in substances, and there is a division of the substances involved into agents and patients. Instead of there being a single form involved in projectile motion – the form of heaviness, responsible for natural motion downwards – there are two, weight and impetus, and the two conflict. The basic ontology is still the same, and the division into agents and patients, though its details may have changed, still persists. Furthermore, despite persistent doubts, there is still something of a distinction between motion and rest, and motion can only be the result of agency. Contrast this with Galileo’s or – still more – Newton’s account: here uniform motion and rest are treated on an equal footing, and, consequently, there can be no unequivocal distinction between motion and rest. So, although Buridan and Oresme are – in some sense – precursors of Galileo, their causal ontology is still, in important respects, thoroughly medieval (Maier 1964).