Chapter III. How definition is destroyed by inspecting its parts, which are genus and difference.

CHAPTER III. How definition is destroyed by inspecting its parts, which are genus and difference.

But the second place taken in common, by which definition can be destroyed, is through inspection toward the very parts of definition and toward those things from which definition exists with respect to substance; from this common consideration many special considerations are drawn. And first, by inspecting genus, whether genus is not posited, whether a certain and determinate genus is not posited, and whether the proximate genus is not posited.

Therefore one must first inspect whether, when the defined thing is in a genus, through the assigned definition it has not been located or placed in some genus. For there is error in all definitions of this sort in which, first or prior in the order of the parts of definition in the account, that is, in the definition itself, there is not posited a genus which is predicated in what, because its essential differences are those which form it into a qualified what, which is the species. In this way the definition of body errs when it is said that body is what has three dimensions; for "what" is an indefinite name and says no genus through which body may be separated from other genera. Or if one wishing to define man said that man is one who knows how to number, because alone among animals he knows how to number; for here no genus has been posited in the definition. But genus, as we have said, wishes to signify what being is, to which an added difference makes a qualified what, which is species, which without genus is not a what but only of what quality, because it is not a formed what. And therefore genus is placed first of those things which are placed in the definition, and as the first subject and the first thing standing under the differences forming and distinguishing it.

Furthermore, one must still inspect whether something must be defined from its genus toward several things as toward ends; for when that which is defined is said toward several things from its very genus, one must consider whether someone in the assigned definition has not assigned it toward all the things toward which it has been stated; for then he has erred, and the definition is destroyed. The example of this is that, if someone wishing to define grammar says that it is the science of writing, he has posited a genus here, but he has not posited all the things toward which grammar is a science. For it still needs to be added that grammar is the science of knowing through construction related to understanding; and thus grammar is the science of writing and of knowing that which is uttered in speech and in the parts of speech, and one who assigns the perfect definition of grammar declares that grammar is a science no more of writing than of understanding. On account of this he who posits something, that is, one of those two, does not define. But he truly defines grammar who has stated both of these things toward which the definition is entire in this way: grammar is the science of rightly writing and rightly understanding what is uttered in speech and in the parts of speech. The reason for this is that there cannot be several substantial definitions of the same thing; and if it is defined toward one, it is defined by the same account toward the other, when each belongs through its genus and not by accident; and thus there will not happen to be several and diverse definitions of the same thing. But genus is something else as science is toward the thing known.

Therefore in some cases, indeed, it necessarily has itself so that one must define toward both things toward which it is, when without these the genus is not perfectly determined, as has been said. But in some cases it is not so. And therefore the consideration needs not correction, but determination made through distinction, as in certain cases where genus is not said through itself toward both, but toward one through itself and toward the other by accident, as medicine is said to be a science for making health and sickness. For concerning this, or toward this, namely to make health, it is said through itself, because this is the science of making health. But concerning that which is to make sickness, it is by accident. But simply, that is, through itself, to make sickness is alien to medicine. On account of this, the one who defined medicine toward both by saying that medicine is the science for making health and sickness did not define medicine any more than if he had defined it toward the other thing, which is to make health, because it is not for making sickness except on account of health, when sickness is the cause of health and of longer life; and it is already known from the science of the Posterior Analytics that where one thing is for the sake of another, in either place there is only one. But perhaps, by inspecting subtly, he defined worse who defined toward both than if he had defined toward one alone, because also any of the rest or of others, and any physician of any art or science, can make sickness, either by wounding or by filling the body immoderately or by exercising it immoderately or by doing something of this sort; for neither science nor art is required for this, since it is not difficult and good.

Furthermore, still by inspecting genus, which is an element, one who wishes to destroy a definition should consider whether, in the definition made from genus, he has assigned toward one something which is toward several things that are unequal according to good and evil, not toward the better but toward the worse, although there are several things toward which what he defined is said to be taken according to genus. For every science and every power said toward another, whether it is natural or artificial or even political, belongs to that which is best in that order according to which it is said toward that thing; and therefore it must be defined toward that according to its genus. Or there is still error with respect to genus by inspecting whether the defined thing, through the assigned definition, has not been placed in its proper genus; whether it has truly been placed in its proper genus or not must be considered from those elements or principles which were introduced in the fourth book of this science. But it was said before when it is placed in an equivocal or analogous term as in a genus.

Again, still by inspecting genus, definition is destroyed if the one assigning the definition has said those things to be genera which transcend, that is, which are not proximate to the defined thing, but he posits superior things while intermediate and ultimate things have been omitted. The example of this is that one wishing to define justice as a special virtue says that justice is a habit affective or distributive of equality, because in communicating or distributing it makes equality, but not according to arithmetical or geometrical middle. One who has defined in this way transcends the proximate genus; for he has left behind virtue, which is the proximate genus of justice, and has not stated what the being of justice is, because although he states what the being of justice is in a remote genus, this is only infinitely and indeterminately. Therefore either the proximate genus must be posited, or all differences must be added to the superior genus, because they draw it all the way to the proximate genus whose difference constitutes the species, since a transcendent difference of a genus joined to that genus does not complete the definition. Hence a definition is not completed from a remote genus; but both are conjoined as potency and genus toward the defined thing itself, for the substance and what of each defined thing is in its own genus, as we have often said. But this which has been said, to place the defined thing in a transcending genus, is the same as not placing it in the proximate genus. For he who said virtue to be the genus of justice, in defining justice, also stated habit, because the superior is said in the inferior and not conversely, as has often been said. And therefore because the definition, in defining, posited the proximate genus, in the proximate genus it stated all superior genera and things transcending the proximate genus, because all superior genera are predicated through themselves of inferiors and are and are said in them at least implicitly. On account of this, the defined thing must either be placed in the proximate genus, or, if a transcendent genus is posited, then all the superior differences of the superior genera must be added to the remote genus, which narrow the remote genus to the proximate genus; because through these, added in this way to the remote genus, the proximate genus is determined and delimited. And then the definition of the proximate genus is posited, and this stands in the definition in place of it. For in this way, with the premises made, he has omitted nothing of those things which pertain from the genus to the proximate genus or to the constitution of the proximate genus; but the pronoun of the proximate genus stated in the definition of the species will be the inferior genus through its constitution. As if, in defining man, I say that man is corporeal, animated, sensible, rational, mortal substance. But he who, in defining, states only the superior genus without the addition of contracting differences, by saying the superior genus in this way, does not state the inferior, because the inferior is in its superior only in potency and indefinitely, and is not in it in act and understanding. For one who says plant, which is a superior genus, does not state tree except in potency and infinitely. And therefore one is not defined into the superior genus. But know that one assigning a definition through a remote genus and contracting through differences, although he does not destroy the definition according to substance, destroys it with respect to the goodness of definition, because he has not posited the difference as he ought ¹.