 Against the “causal” theory of perception (effectively, representative realism), Price argues that the concept of cause is neither necessary nor sufficient for our belief in physical objects, that even in spatial perception only in some cases do sense data resemble physical objects, and that in any case material objects are not inferred from sense data. He further maintains that although sense data are distinct from material objects (contra naïve realism) and their existence may require the existence of minds, they are not mental (1932: 117–127, 316–317). He elaborates notions of perceptual acceptance and perceptual assurance to describe the non-inferential cognitive acts through which we accept and believe that material objects exist. The belief in material objects consists in (a) the construction of a “standard solid” from sense data, which is a spatial structure that fits the outer shape of a physical object in three dimensions, together with (b) belief in a causally efficacious “physical occupant” of this location (1932: ch.  8).[16]