English: Composition and Literature

by W. F. Webster

[93] A definition may be faulty in its differentia also. The differentia is that part of a definition which names the difference between the term defined and the general class to which it belongs. “Man is a reasoning animal.” “Animal” names the general class, and “reasoning” is the differentia which separates “man” from other “animals.” On the selection of this limiting word depends the accuracy of the definition. “Man is an animal that walks,” or “that has hands,” or “that talks,” are all faulty; because bears walk, monkeys have hands, and parrots talk. Supposing the following definitions were given: “A cat is an animal that catches rats and mice;” “A rose is a flower that bears thorns;” “Gold is a metal that is heavy;” all would be faulty because the differentia in each is faulty. Notice, too, the definitions of “dog” and “canine” already given. Even “man is a reasoning animal” may fail; since many men declare that other animals reason. The differentia should include all the members that the term denotes, and it should exclude all that it does not denote.

Requisites of a good Definition. The requisites of a good definition are: first, that it shall include or denote all the members of the class; second, that it shall exclude everything which does not belong to its class; third, that the words used in the definition shall be better understood than the word defined; fourth, that it shall be brief.

A definition may perfectly expound a term; and because of the very qualities that make it a good definition, accuracy and brevity, it may be almost valueless to the ordinary reader. For instance, this definition, “An acid is a substance, usually sour and sharp to the taste, that changes vegetable blue colors to red, and, combining with an earth, an alkali, or a metallic [94] oxide, forms a salt,” would not generally be understood. So it frequently becomes necessary to do more than give a definition in order to explain the meaning of a term. This brings us to the study of exposition, as it is generally understood, in which all the resources of language are called into service to explain a term or a proposition.

How do Men explain? First, by Repetition. What, then, are the methods of explaining a proposition? First, a proposition may be explained by the repetition of the thought in some other form. To be effective, repetition must add something to what has been said; the words used may be more specific or they may be more general. For example, “A strong partisan may not be a good citizen. The stanchest Republican may by reason of a blind adherence to party be working an injury to the country he loves. Indeed, one can easily conceive a body of men so devoted to a theory, beautiful though it may be in many respects, that they stand in the way of the world’s progress.” The second sentence repeats the thought of the first in more specific terms; the third repeats it in more general terms. The specific may be explained by the general; more often the general is cleared up by the specific. In either case, the proposition must be brought one step nearer to the reader by the restatement, or the repetition is not good.

Speaking of written or printed words, Barrett Wendell writes:—

“In themselves, these black marks are nothing but black marks more or less regular in appearance. Modern English type and script are rather simple to the eye. Old English and German are less so; less so still, Hebrew and Chinese. But all alphabets present to the eye pretty obvious traces of regularity; in a written or printed page the same mark will [95] occur over and over again. This is positively all we see,—a number of marks grouped together and occasionally repeated. A glance at a mummy-case, an old-fashioned tea-chest, a Hebrew Bible, will show us all that any eye can ever see in a written or printed document. The outward and visible body of style consists of a limited number of marks which, for all any reader is apt to know, are purely arbitrary.” (“English Composition.”)

In this paragraph every sentence is a repetition of some part of the opening or topic sentence, and serves to explain it.

Second, by telling the obverse. Second, a proposition may be explained by telling what it is not. At times this is as valuable as telling what it is. Care should be taken that the thing excluded or denied have some likeness to the proposition or term being explained; that the two be really in some danger of being confused. Unless to a hopelessly ignorant person, it would not explain anything to say “a horse is not a man;” but to assert that “a whale is not a fish, though they have many points in common,” would prepare the way for an explanation of what a whale is. The obverse statement is nearly always followed by a repetition of what the thing is.

The following from Newman illustrates the method:

“Now what is Theology? First, I will tell you what it is not. And here, in the first place (though of course I speak on the subject as a Catholic), observe that, strictly speaking, I am not assuming that Catholicism is true, while I make myself the champion of Theology. Catholicism has not formally entered into my argument hitherto, nor shall I just now assume any principle peculiar to it, for reasons which will appear in the sequel, though of course I shall use Catholic language. Neither, secondly, will I fall into the fashion of the day, of identifying Natural Theology with Physical [96] Theology; which said Physical Theology is a most jejune study, considered as a science, and really no science at all, for it is ordinarily no more than a series of pious or polemical remarks upon the physical world viewed religiously, whereas the word ‘Natural’ comprehends man and society, and all that is involved therein, as the great Protestant writer, Dr. Butler, shows us. Nor, in the third place, do I mean by Theology polemics of any kind; for instance, what are called ‘Evidences of Religion,’ or ‘the Christian Evidences.’... Nor, fourthly, do I mean by Theology that vague thing called ‘Christianity,’ or ‘our common Christianity,’ or ‘Christianity the law of the land,’ if there is any man alive who can tell what it is.... Lastly, I do not understand by Theology, acquaintance with the Scriptures; for, though no person of religious feeling can read Scripture but he will find those feelings roused, and gain much knowledge of history into the bargain, yet historical reading and religious feeling are not a science. I mean none of these things by Theology. I simply mean the Science of God, or the truths we know about God put into a system; just as we have a science of the stars, and call it astronomy, or of the crust of the earth, and call it geology.”[15]