Yet species and genus do not merely indicate quality, like the term ‘white’; ‘white’ indicates quality and nothing further, but species and genus determine the quality with reference to [20] a substance: they signify substance qualitatively differentiated. The determinate qualification covers a larger field in the case of the genus that in that of the species: he who uses the word ‘animal’ is herein using a word of wider extension than he who uses the word ‘man’. Another mark of substance is that