Also, see if he has put anything that is precious or desirable for its own sake into the class ‘capacity’ or ‘capable’ or ‘productive’ of anything. For capacity, and what is capable or productive of anything, is always desirable for the sake of something else.
Or see if he has put anything that exists in two genera or more into one of them only. For some things it is impossible to place in a single genus, e.g. the ‘cheat’ and the ‘slanderer’: for neither he who has the will without the capacity, nor he who has the capacity without the will, is a slanderer or cheat, but he who has both of them. Hence he must be put not into one genus, but into both the aforesaid genera.
Moreover, people sometimes in converse order render genus as differentia, and differentia as genus, defining (e.g.) astonishment as ‘excess of wonderment’ and conviction as ‘vehemence of conception’. For neither ‘excess’ nor ‘vehemence’ is the genus, but the differentia: for astonishment is usually taken to be an ‘excessive wonderment’, and conviction to be a ‘vehement conception’, so that ‘wonderment’ and ‘conception’ are the genus, while ‘excess’ and ‘vehemence’ are the differentia. Moreover, if any one renders ‘excess’ and ‘vehemence’ as genera, then inanimate things will be convinced and astonished. For ‘vehemence’ and ‘excess’ of a thing are found in a thing which is thus vehement and in excess. If, therefore, astonishment be excess of wonderment the astonishment will be found in the wonderment, so that ‘wonderment’ will be astonished! Likewise, also, conviction will be found in the conception, if it be ‘vehemence of conception’, so that the conception will be convinced. Moreover, a man who renders an answer in this style will in consequence find himself calling vehemence vehement and excess excessive: for there is such a thing as a vehement conviction: if then conviction be ‘vehemence’, there would be a ‘vehement vehemence’. Likewise, also, there is such a thing as excessive astonishment: if then astonishment be an excess, there would be an ‘excessive excess’. Whereas neither of these things is generally believed, any more than that knowledge is a knower or motion a moving thing.
Sometimes, too, people make the bad mistake of putting an affection into that which is affected, as its genus, e.g. those who say that immortality is everlasting life: for immortality seems to be a certain affection or accidental feature of life. That this saying is true would appear clear if any one were to admit that a man can pass from being mortal and become immortal: for no one will assert that he takes another life, but that a certain accidental feature or affection enters into this one as it is. So then ‘life’ is not the genus of immortality.
Again, see if to an affection he has ascribed as genus the object of which it is an affection, by defining (e.g.) wind as ‘air in motion’. Rather, wind is ‘a movement of air’: for the same air persists both when it is in motion and when it is still. Hence wind is not ‘air’ at all: for then there would also have been wind when the air was not in motion, seeing that the same air which formed the wind persists. Likewise, also, in other cases of the kind. Even, then, if we ought in this instance to admit the point that wind is ‘air in motion’, yet we should accept a definition of the kind, not about all those things of which the genus is not true, but only in cases where the genus rendered is a true predicate. For in some cases, e.g. ‘mud’ or ‘snow’, it is not generally held to be true. For people tell you that snow is ‘frozen water’ and mud is earth mixed with moisture’, whereas snow is not water, nor mud earth, so that neither of the terms rendered could be the genus: for the genus should be true of all its species. Likewise neither is wine ‘fermented water’, as Empedocles speaks of ‘water fermented in wood’;’ for it simply is not water at all.
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6
Moreover, see whether the term rendered fail to be the genus of anything at all; for then clearly it also fails to be the genus of the species mentioned. Examine the point by seeing whether the objects that partake of the genus fail to be specifically different from one another, e.g. white objects: for these do not differ specifically from one another, whereas of a genus the species are always different, so that ‘white’ could not be the genus of anything.
Again, see whether he has named as genus or differentia some feature that goes with everything: for the number of attributes that follow everything is comparatively large: thus (e.g.) ‘Being’ and ‘Unity’ are among the number of attributes that follow everything. If, therefore, he has rendered ‘Being’ as a genus, clearly it would be the genus of everything, seeing that it is predicated of everything; for the genus is never predicated of anything except of its species. Hence Unity, inter alia, will be a species of Being. The result, therefore, is that of all things of which the genus is predicated, the species is predicated as well, seeing that Being and Unity are predicates of absolutely everything, whereas the predication of the species ought to be of narrower range. If, on the other hand, he has named as differentia some attribute that follows everything, clearly the denotation of the differentia will be equal to, or wider than, that of the genus. For if the genus, too, be some attribute that follows everything, the denotation of the differentia will be equal to its denotation, while if the genus do not follow everything, it will be still wider.
Moreover, see if the description ‘inherent in S’ be used of the genus rendered in relation to its species, as it is used of ‘white’ in the case of snow, thus showing clearly that it could not be the genus: for ‘true of S’ is the only description used of the genus in relation to its species. Look and see also if the genus fails to be synonymous with its species. For the genus is always predicated of its species synonymously.
Moreover, beware, whenever both species and genus have a contrary, and he places the better of the contraries inside the worse genus: for the result will be that the remaining species will be found in the remaining genus, seeing that contraries are found in contrary genera, so that the better species will be found in the worse genus and the worse in the better: whereas the usual view is that of the better species the genus too is better. Also see if he has placed the species inside the worse and not inside the better genus, when it is at the same time related in like manner to both, as (e.g.) if he has defined the ‘soul’ as a ‘form of motion’ or ‘a form of moving thing’. For the same soul is usually thought to be a principle alike of rest and of motion, so that, if rest is the better of the two, this is the genus into which the soul should have been put.
Moreover, judge by means of greater and less degrees: if overthrowing a view, see whether the genus admits of a greater degree, whereas neither the species itself does so, nor any term that is called after it: e.g. if virtue admits of a greater degree, so too does justice and the just man: for one man is called ‘more just than another’. If, therefore, the genus rendered admits of a greater degree, whereas neither the species does so itself nor yet any term called after it, then what has been rendered could not be the genus.
Again, if what is more generally, or as generally, thought to be the genus be not so, clearly neither is the genus rendered. The commonplace rule in question is useful especially in cases where the species appears to have several predicates in the category of essence, and where no distinction has been drawn between them, and we cannot say which of them is genus; e.g. both ‘pain’ and the ‘conception of a slight’ are usually thought to be predicates of ‘anger in the category of essence: for the angry man is both in pain and also conceives that he is slighted.