Castañeda started from the fact that thoughts about real things in the world are of a fundamentally similar nature to thoughts about things in the imagination, it is still a thought, and from there he hypothesized an entire realm of abstract objects (he calls it "abstractist ontology") that included both the real and the imagined. He referred to these objects collectively as "guises", and argued that they could be treated as sets of properties. He went on to develop the guise theory of intentionality and analyse all of language and perception in terms of these guises, ultimately developing an entire metaphysics based on them.