Definition, Division, and Doubt

The openings and the sources of our questions have to do with these points and lie within them. But before we come to definitions, demonstrations, and divisions, we must set out in what way the question is being asked. Words that carry more than one meaning have to be dealt with, and words that carry the same meaning have to be stated exactly, according to what each of them signifies. Then we must ask whether the proposition belongs among the things considered in relation to something else, or is taken by itself. Further: whether it is, what it is, and what happens to it — or, put another way, whether it is, what it is, and why it is. Toward examining these points, knowing particulars and universals, antecedents and differences, and the divisions of them, all help. [a]

Induction aims at the general statement and at the definition; the divisions give us the species, and what a thing is, and the individual. Considering how a thing is leads us to take up what is peculiar to it, and raising difficulties brings out the particular differences and the demonstrations, and in other ways enlarges the inquiry and what follows from it; and the result of the whole is knowledge and truth. Again, the summing up that comes out of division becomes a definition. For a definition is taken up both before division and after it: before, when it is granted or simply stated; after, when it has been demonstrated. And it is by sense perception that the universal is gathered up out of the particular, since induction begins at sense perception and ends at the universal. Induction, then, shows not what a thing is, but that it is or is not. Division shows what it is. Definition, like division, teaches the essence and what a thing is, but not whether it is; while demonstration explains all three — whether it is, what it is, and why it is.

There are also definitions that include the cause. And since a thing can be known when we see it, that is, when we see its cause, and since the causes are four — the matter, the moving power, the form, and the end — definition will be fourfold. So we must first take the genus, which holds within it the points nearest to those above it, and after that the difference that comes next. The run of differences, cut and divided one after another, completes the answer to “What is it?” There is no need to state every difference belonging to a thing, only those that make up the species.

Analysis and synthesis in geometry work like division and definition in logic, and by dividing we get back to what is simple and more elementary. So we divide the genus of whatever has been proposed for examination into the species contained in it. In the case of a human being, for instance, we divide “animal,” which is the genus, into the species that appear in it: the mortal and the immortal. And by going on dividing the genera that look composite into simpler species, we arrive at the point we are investigating, which admits of no further division. For after dividing “the animal” into mortal and immortal, we divide it next into land animals and water animals, and the land animals again into those that fly and those that walk; and so, dividing the species that stands nearest to what we are looking for and also contains what we are looking for, we arrive by division at the simplest species, which contains nothing else but the thing we are after. For again we divide what walks into the rational and the irrational; and then, selecting from the species grasped by division those nearest to the human being, and combining them into a single formula, we state the definition of a human being, who is an animal — mortal, land‑dwelling, walking, rational.

So division supplies the class that serves as matter, looking for the definition in the simplicity of the name; while the definition, the work of the craftsman and maker, by putting together and building up, presents the knowledge of the thing as it is — not of those things of which we have only general notions. To those notions, we say, explanatory phrases belong; for divisions apply to those notions too. Now one kind of division divides what is divided into species, taking it as a genus; another into parts, taking it as a whole; and another into accidents. The division of a whole into its parts is for the most part thought of with reference to size, and the division into accidents can never be fully worked out, if essence must necessarily be present in each of the things that are. So both of these divisions are to be set aside, and only the division of a genus into species is approved, the division by which both the sameness that lies in the genus and the diversity that lies in the specific differences are marked out.

A species is always looked at within a part. The converse, however, does not hold: if a thing is part of another, it will not for that reason also be a species. A hand is part of a human being, but it is not a species. And the genus is present in the species, for it is in the human being and in the ox alike. But the whole is not present in the parts, for the man is not in his feet. That is why a species counts for more than a part, and why whatever is said of the genus will all be said of the species as well. It is best, then, to divide the genus into two species, or if not into two, into three. The species, divided in this more general way, are marked out by sameness and by difference; and when they are divided further, they are marked out by the features indicated generically. For each of the species is either an essence — as when we say that some essences are bodily and some bodiless — or a how much, or a relation, or a where, or a when, or a doing, or a being acted upon.

A person, then, will be able to give the definition of whatever he actually knows, since no one can be acquainted with something he cannot take in and mark off in words. And it is out of ignorance of the definition that so many disputes and deceptions arise. For if the man who knows a thing has the knowledge of it in his mind, and can explain in words what he has in mind, and if the explanation of the thought is a definition, then whoever knows a thing must necessarily be able to give its definition. Now in definitions a difference is taken up, and in the definition it stands in the place of a sign. So when the capacity for laughter is added to the definition of a human being, it makes the whole: a rational, mortal, land‑dwelling, walking, laughing animal. For the things added to a definition by way of difference are signs of a thing’s properties; they do not show the nature of the things themselves. They say that the difference is the assigning of what is peculiar to a thing; and since whatever has the difference differs from everything else, what belongs to it alone, and is stated convertibly with the thing, must in definitions be taken up by the first genus as principal and fundamental.

Accordingly, in the longer definitions the species that are found are as many as the ten categories, while in the shortest the chief points of the nearest species are taken and mark out the essence and nature of the thing. The shortest consists of three terms: the genus and two species that are strictly necessary. And this is done for the sake of brevity. So we say: a human being is the laughing animal. And we must take up whatever belongs above all to the thing being defined, or its characteristic excellence, or its characteristic function, or something of that kind. Accordingly, while a definition explains the essence of a thing, it cannot take in its nature exactly. By means of the chief species the definition sets out the essence, and comes close to holding the essence within a quality.

Two things above all produce skepticism. The first is the changeableness and instability of the human mind, whose nature it is to breed disagreement — either of one person with another, or of people with themselves. The second is the inconsistency there is in things, which, as one would expect, tends to produce skepticism. For we cannot believe all the views, because they conflict with one another. We cannot disbelieve them all, because the view that says all of them are untrustworthy is itself one of them, and so untrustworthy along with them. And we cannot believe some and disbelieve others, because they balance each other out. So we are driven to skepticism. [i]

But chief among the causes of skepticism is that instability of the mind which produces disagreement; and disagreement is the nearest cause of doubt. That is why life is full of courts and councils, and, in short, of choosing between what is called good and what is called bad — all of them signs of a mind in doubt, limping along in weakness because the matters before it conflict. And there are libraries full of books, and compilations and treatises by people who differ in their doctrines and are confident that they themselves know the truth that is in things.

In language there are three things. Names, which are in the first place the symbols of our conceptions, and by way of those also of the things themselves. Second, conceptions, which are the likenesses and imprints of the things. That is why conceptions are the same in everyone, since the same imprint is produced in everyone by the things; but names are not the same, because languages differ. And third, the things themselves, by which the conceptions are imprinted in us. Grammar reduces names to the twenty‑four general elements, for the elements have to be fixed. Of particulars there is no knowledge, since they are unlimited; it belongs to knowledge to rest on general and defined principles. That is why particulars are resolved into universals. Philosophical inquiry occupies itself with conceptions and with real things; but since the particulars of these are unlimited, certain elements have been found under which every subject of investigation is brought. If a thing can be shown to fall under one or more of the elements, we prove that it exists; if it escapes them all, we prove that it does not. [l]

Of things said, some are said without being combined — “man,” for instance, and “runs,” and anything else that does not complete a sentence capable of being true or false. And of things said in combination, some point out essence, some quality, some quantity, some relation, some where, some when, some position, some having, some doing, and some being acted upon. These we call the elements of material things, after the first principles, for they can be examined by reason. Immaterial things, on the other hand, can be grasped by the mind alone, by a direct application of it. And of the things classed under the ten categories, some are stated on their own account — the nine categories — and others in relation to something else.

Again, of the things contained under these ten categories, some are univocal, such as ox and man, so far as each is an animal. Univocal terms are those to which a common name belongs, “animal,” along with the same account, that is, the same definition: living essence. Heteronyms are terms that belong to the same subject under different names, such as going up and going down, for the road is the same whether you take it upward or downward. There is another kind of heteronym as well, such as horse and black, terms that have a different name and a different definition from each other and do not have the same subject; but these are to be called different, not heteronyms. Polyonyms are terms that have the same definition but a different name, such as blade, sword, and saber. And paronyms are terms named from something else, as “manly” is named from “manliness.”

Equivocal terms have the same name but not the same definition, as “man” is used of both the living animal and the picture of one. Of equivocal terms, some get their shared name by chance, like the two men called Ajax, the Locrian and the Salaminian; and some get it by intention. Of these, some are named from resemblance, as “man” is used of both the living man and the painted one; some from analogy, as the foot of Mount Ida and our own foot, because both are underneath; and some from what they do, as the foot of a ship, by which the ship sails, and our foot, by which we move. Equivocal terms are also named from one and the same source and with reference to one and the same thing, as a book and a scalpel are both called surgical — from the surgeon who uses them, and with reference to the work of surgery itself.