 The basic hypothesis is that bodies need nothing other than determinate sizes, figures, etc. in order to arouse tastes, etc. in beings that have sensitive organs. Without ears, tongues, and skin around armpits, there are no sounds, tastes, or tickles but only various shapes, motions,  etc.[1]  In particular, some bodies are constantly divided into tiny particles; some of them rise, enter the nasal passages and start a process that ends with odors; others fall onto the surface of the tongue, mix with saliva and eventually produce tastes; tiny vibrations that pervade the air make contact with the ear drums which connect with other organs that produce sounds; finally, there is a particular sort of igneous particle found in fire which moves through pores of the body and makes us warm. Many observations are brought in support of these hypotheses (Galileo 1623 [2003: 188–9]). Thought experiments establish the possibility of this account. Two features of the hypothesis are particularly important. First, it sketches a program of explanation for natural philosophy in which the distinction of PQs and SQs has an essential part (Crombie 1972: 80–7). Second, it entails that SQs are not in bodies that cause them but internal to sentient bodies—effects of the mechanical affections of insensient bodies on the sensory organs of living bodies. Piccolino and Wade (2008: 1218–19, 1319–21) portray Galileo as advocating the sort of explanatory program urged later by Hermann Helmholtz and presently pursued in neuro-psychology. (On Helmholtz’ version of the P/SQ distinction, see Hatfield 2011.)