 Imagination was a matter of material images being formed in the brain. But, it was held by Boyle and others, we have knowledge of things which are literally unimaginable — that is, they cannot be accurately represented by a corporeal image in the central nervous system. There were a variety of reasons for this belief. First it was held that there were things which were too large, and things which were too small to be imagined, that is, imaged. Hence some non-material faculty was needed to account for this ability. Additionally, there are things which are not image-able because they cannot be represented accurately by any physical system. Boyle’s stock example in this area, though not his only example, is the incommensurability of the sides and diagonal of a square. Since \(\sqrt{2}\) is irrational no discrete (corpuscular) system can accurately represent both. But we do have knowledge of squares. Therefore we must be employing a non-material system. Also, there were things such as Descartes’ chiliagon which, while they could be represented physically, could not (as experience shows) be represented accurately by our physical imaging system.