 This conclusion does not say whether sense data are mental or physical (1977: 119). The argument that sense data are all mental proceeds for the case of vision by seeking to establish that colors are mental items. The argument is indirect, from the conclusion that colors are not physical. This conclusion, in turn, relies on the claim that color is not a “scientific property”, that only scientific properties exist in the external world and affect the eyes and brain, and that color then can only be a mental entity caused by neural activity (1977: ch. 5).