The division of labour between the ontic conception and the pragmatics of presenting explanations is thus as follows: the former delimits the ‘stuff or content of explanation, the latter investigates the ways in which this can be purveyed. Causal processes ‘fill in the gaps’ between all the events in the mechanism, and they do so in two quite different, though complementary, senses. The general issue is whether it is possible to come up with a concept of a non-causal mechanism which might enable people to understand examples of this kind. The reason why the virtual particles leave no tracks is because they are not allowed by the uncertainty relations to interact with anything. Nevertheless, Aristotelian explanations of how bodies moved from one place to another were given with reference to laws: laws about the nature of natural and violent motion.