According to the Cambridge Platonist Henry More, individual spirits--the souls of humans and non-human animals--are extended but cannot be physically divided. His contemporaries and recent commentators have charged that More has never given an explication of the grounds on which the indivisibility of spirits is based. In this article, I suggest that exploring the usage that More makes of the analogy between spirits and light could go some way towards providing such an explication. More compares the relation between spirit and (...) matter to the relation that, according to Aristotelian theories of light, holds between ?intentional species? and matter. I will argue that the purpose of his comparison is to highlight that both intentional species and spirits are existentially independent from matter. The existential independence of intentional species from matter expresses itself in the fact that light is not moved through the motion of the illuminated body. The existential independence of spirits from matter expresses itself in the fact that when a body that is coextensive with a spirit is divided, the spirit is not thereby divided but rather contracts into the remaining living organism. (shrink)