 Ockham denies species not on the basis of empirical evidence, or on the basis of epistemological arguments, but purely and simply on the basis of his razor: if we deny species, then we can give an account of the phenomena which uses fewer entities, because species are entities. Although this position of Ockham’s did not have much influence on his contemporaries or followers – it is, after all, extremely implausible – it is a good example of how causal reasoning is affected by tacit ontological assumptions: the fact that species were seen as entities and the fact that Ockham had a programme of reducing the number of entities, led to an account of perception which tried to do away with species. On the other hand, action at a distance was, despite its implausibility, entirely unaffected by Ockham’s critique. And, similarly, Ockham’s account was not noticeably simpler than the accounts it criticised, which shows how far Ockham’s own razor was from the principles of simplicity and the like, which are usually considered to be its modern equivalents.