as animals are concerned, is characterised generally by the power of sentience, in man it is characterised by that of sentience, or of rationality (the faculty of course being referred to the actual operation of the faculty, certainly the main point is the actual operation of it); so that living seems mainly to consist in the act of sentience or exerting rationality: now the fact of living is in itself one of the things that are good and pleasant (for it is a definite totality, and whatever is such belongs to the nature of good), but what is naturally good is good to the good man: for which reason it seems to be pleasant to all. (Of course one must not suppose a life which is depraved and corrupted, nor one spent in pain, for that which is such is indefinite as are its inherent qualities: however, what is to be said of pain will be clearer in what is to follow.)
If then the fact of living is in itself good and pleasant (and this appears from the fact that all desire it, and specially those who are good and in high happiness; their course of life being most choice-worthy and their existence most choice-worthy likewise), then also he that sees perceives that he sees; and he that hears perceives that he hears; and he that walks perceives that he walks; and in all the other instances in like