In order to remain on a metaphysical plane and resist physicalist notions of mediality, the idea of a "modality" is introduced, a supra-medial ideal form of aesthetic organization. With Arnheim's help, Robert Sowers outlined three spatial modalities: the Picture, Sculpture and Architecture. A mixture of two modalities or one conceived in the mode of another is considered a hybrid. Arnheim spent a good bit of time discussing how modalities might differ, often by imagining each put to different uses (essentially the phenomenological method of imaginative variation). Spatial hybrids are all objects of vision and therefore require substantial differentiation, whereas temporal modalities are easier, owing to the fact that visual action, text and music are relatively distinct.