I start with Cornford's diagnosis of Plato's view of the perceptible world and perception. Cornford reacted with justification against Taylor's assimilation of Timaeus to a modern positivistic view of science. Taylor had suggested that the status of our accounts of the natural world as merely likely could ultimately be overcome with the progress of empirical science. The Timaeus story was for Taylor a myth only ‘in the sense that it is the nearest approximation which can “provisionally” be made to exact truth’.Cornford was surely right to object that our accounts could in principle only ever be likely in so far as they are accounts of a likeness.

Cornford's and Taylor's positions are contraries but not contradictories. For whilst mutually exclusive, they are not jointly exhaustive. Whilst Taylor gives too much to perception, I want to argue that Cornford gives too little. In natural philosophy perception stands in a complex interactive relationship with reason. It is the aim of this chapter to analyse this relationship.