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 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 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 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]

Third, by Details.

Third, _a common way of explaining a proposition is to go into particulars about it._ Enough particulars should be given to furnish a reasonable explanation of the proposition. Macaulay, writing of the "muster-rolls of names" which Milton uses, goes into details. He says:--

"They are charmed names. Every one of them is the first link in a long chain of associated ideas. Like the dwelling place of our infancy revisited in manhood, like the song of our country heard in a strange land, they produce upon us an effect wholly independent of their intrinsic value. One transports us back to a remote period of history. Another places us among the novel scenes and manners of a distant region. A third evokes all the dear classical recollections of childhood,--the schoolroom, the dog-eared Virgil, the holiday, and the prize. A fourth brings before us the splendid phantoms of chivalrous romance, the trophied lists, the embroidered housings, the quaint devices, the haunted forests, the enchanted gardens, the achievements of enamoured knights, and the smiles of rescued princesses."[16]

Fourth, by Illustrations.

Fourth, _a proposition may be explained by the use of a single example or illustration._ The value of this method depends on the choice of the example. It must in no essential way differ from the general case it is intended to illustrate. Supposing this proposition were advanced by some woman-hater: "All women are, by nature, liars," and it should be followed by this sentence, "For example, take this lady of fashion." Such an illustration is worthless. The individual chosen does not fairly represent the class. If, on the other hand, a teacher in physics should announce that "all bodies fall at the same rate in a vacuum," and should illustrate by saying, "If I place a bullet and a feather in a tube from which the air has been exhausted, they will be found to fall equally fast," his example would be a fair one, as the two objects differ in no manner essential to the experiment from "all bodies."

Here should be included anecdotes used as illustrations. They are of value if they are of the same type as the general class they are intended to explain. They may be of little value, however. It could safely be said that half the stories told in campaign speeches are not instances in point at all, but are told only to amuse and deceive.

Specific instances must be chosen with care if they are to serve a useful purpose in exposition.

This example is from Newman:--

"To know is one thing, to do is another; the two things are altogether distinct. A man knows that he should get up in the morning,--he lies abed; he knows that he should not lose his temper, yet he cannot keep it. A laboring man knows that he should not go to the ale-house, and his wife knows that she should not filch when she goes out charing, but, nevertheless, in these cases, the consciousness of a duty is not all one with the performance of it. There are, then, large families of instances, to say the least, in which men may become wiser, without becoming better."[17]

Fifth, by Comparisons.

Last, _a thing may be explained by telling what it is like, or what it is not like._ This method of comparison is very frequently employed.

To liken a thing to something already known is a vivid way of explaining. Moreover in many cases it is easier than the method of repetition or that of details. By this method Macaulay explains his proposition that "it is the character of such revolutions that we always see the worst of them first." He says:--

"A newly liberated people may be compared to a northern army encamped on the Rhine or the Xeres. It is said that when soldiers in such a situation first find themselves able to indulge without restraint in such a rare and expensive luxury, nothing is to be seen but intoxication. Soon, however, plenty teaches discretion, and, after wine has been for a few months their daily fare, they become more temperate than they had ever been in their own country. In the same manner, the final and permanent fruits of liberty are wisdom, moderation, and mercy. Its immediate effects are often atrocious crimes, conflicting errors, skepticism on points the most clear, dogmatism on points the most mysterious."[18]

The comparison may be a simile or a metaphor, as when Huxley writes, explaining "the physical basis of life:"--

"Protoplasm, simple or nucleated, is the formal basis of all life. It is the clay of the potter: which, bake it and paint it as he will, remains clay, separated by artifice, and not by nature, from the commonest brick or sun-dried clod."[19]

These, then, are the methods commonly adopted for explaining terms and propositions. First, by the use of definitions; second, by repeating the proposition either directly or obversely, adding something to the thought by each repetition; third, by enumerating particulars which form the ground for the statement; fourth, by selecting an instance which fairly illustrates the proposition; fifth, by the use of comparisons and analogies.

The Subject.

Some general considerations regarding the choice of a subject have been given. A subject should lend itself to the form of discourse employed; next, it should be a subject interesting to the readers; and third, it should be interesting to the writer and suited to his ability. The last condition makes it advisable to limit the subject to a narrow field. Few persons have the ability to view a general subject in all its relations. "Books" everybody knows something of; yet very few are able to treat this general subject in all its ramifications. A person writing of the general topic "books" would not only be compelled to know what a book is, what may truly be called a book, and what is the value of books to readers, and therefore the influence of the different kinds of literature; he would also be driven to study the machinery for making books, the history of printing, illustrating, and binding books, and all the mechanical processes connected with the manufacture of books. The subject might take quite another turn, and be the development of fiction or drama; it might be a discussion of the influences, political or social, that have moulded literature; it might be a study of character as manifested in an author's works. No one is well fitted to write on the general topic "books." A subject should be limited.

The Subject should allow Concrete Treatment.

For young persons _the subject should be so selected and stated that the treatment may be concrete._ As persons advance they make more generalizations; few, however, go so far as to think in general terms.

Macaulay says, "Logicians may reason about abstractions, but the great mass of men must have images." That author depended largely for his glittering effects upon the use of common, concrete things which the masses understand. The subject should be such that it can be treated concretely. "Love," as a general proposition, is beautiful; but what more can a young writer say about it? Let him leave the whole horde of abstract subjects found in old rhetorics alone. They are subjects for experience; they cannot be handled by youth.

The Theme.

After the subject has been chosen, the writer next considers how he shall treat it. He selects the attitude he will assume toward the proposition, his point of view; and this position he embodies in a short sentence, called his _theme._ For instance, "patriotism" is the subject; as it stands it is abstract and very general. However, this, "Can a partisan be a patriot?" would be sufficiently concrete to be treated. Even yet there is no indication of the author's point of view. Should he write, "A real partisan is no patriot," his theme is announced, and his point of view known.

A _theme,_ either explicit or implicit, _is essential in exposition._ It is not necessary that it shall be stated to the reader, but it must be clearly stated by the writer for his own guidance. It is, however, usually announced at the opening of the essay. Whether announced or not, it is most essential to the success of the essay. It is the touchstone by which the author tries all the material which he has collected. Not everything on the subject of patriotism should be admitted to an essay that has for its theme, "A real partisan cannot be a true patriot." It would save many a digression if the theme were always written in bold, black letters, and placed before the author as he writes. Every word in a theme should be there for a purpose, expressing some important modification of the thought. For instance, the statement above regarding a partisan may be too sweeping; perhaps the essayist would prefer to discuss the modified statement that "a blind partisan cannot always be a true patriot." The theme should state exactly what will be treated in the essay. The statement of it should employ the hardest kind of thinking; and when the theme is determined definitely and for all, the essay is safe from the intrusion of foreign ideas which disturb the harmony of the whole.

Another advantage in the theme is that, when once chosen, it will go far toward writing the essay. One great trouble with the young writer is that he is not willing to rely on his theme to suggest his composition. Mr. Palmer well says:--

"He examines his pen point, the curtains, his inkstand, to see if perhaps ideas may not be had from these. He wonders what the teacher will wish him to say, and he tries to recall how the passage sounded in the Third Reader. In every direction but one he turns, and that is the direction where lies the prime mover of his toil, his subject. Of that he is afraid. Now, what I want to make evident is that his subject is not in reality the foe, but the friend. It is his only helper. His composition is not to be, as he seems to suppose, a mass of laborious inventions, but it is made up exclusively of what the subject dictates. He has only to attend. At present he stands in his own way, making such a din with his private anxieties that he cannot hear the rich suggestions of his subject. He is bothered with considering how he feels, or what he or somebody else will like to see on his paper. This is debilitating business. He must lean on his subject, if he would have his writing strong, and busy himself with what it says, rather than with what he would say."[20]

The Title.

Having selected a subject, and with care stated the theme, it yet remains to give the essay a name. There is something in a name, and those authors who make a living by the pen are the shrewdest in displaying their wares under the most attractive titles. _The title should be attractive,_ but it should not promise what the essay does not give. Newspaper headlines are usually attractive enough, but shamefully untruthful. Next, the title should _indicate the scope of the essay._ When Mr. Palmer calls his little book "Self-Cultivation in English," it is evident that it is not a text-book, and that it will not treat English as literature or as a science. Then, the title should be _short._ The theme can rarely be used as a title; it is too long. But the paramount idea developed in the essay should be embodied in the title. "Partisanship and Patriotism" would be a good subject to give the essay we have spoken of. The title, then, should be attractive; it should be short; and it should truthfully indicate the contents of the essay.

Selection of Material.

One of the important factors in the construction of an essay is the selection of material. Though theme and title have already been discussed, it was not because they are the things for a writer to consider next after he has chosen his subject, but because they are so intimately bound up in the subject that their consideration at that time was natural. Before a writer can decide upon the position he will assume toward a proposition, he should have looked over the field in a general way; for only with the facts before him is he competent to choose his point of view and to state his theme. The title is not in the least essential to the writing of the essay; it may be deferred until the essay is finished. It is necessary, however, that the writer have much knowledge of his subject, and that from this knowledge he be able to frame an opinion regarding the subject. When this has been done he is ready to begin the work of constructing his essay; and the first question in exposition, as in narration and description, is the selection of material to develop the theme he has chosen.

The selection of material is a more difficult matter in exposition than in narration and description. It requires the shrewdest scrutiny to keep out matter that does not help the thought forward. In narration we decided by the main incident; in description by the purpose and the point of view; in exposition we test all material by its relation to the theme. Does it help to explain the theme? If not, however good material it may be, it has no business in the essay.

Association of ideas is a law by which, when one of two related ideas is mentioned, the other is suggested. To illustrate, when Manila is mentioned, Admiral Dewey appears; when treason is spoken of, Arnold is in the mind. This law is of fundamental importance in arranging an essay; one thing should suggest the next. But valuable as it is, even indispensable, it may become the source of much mischief. For instance, a pupil has this for a topic, "Reading gives pleasure to many." He writes as his second sentence, "By pleasure I mean the opposite of pain," and goes on. "All things are understood by their opposites. If we did not know sickness, we could not enjoy our health.

Joy is understood through sorrow. I remember my first sorrow. My father had just given me a new knife,--my first knife," and so on from one thing to another. And not so unnaturally either; each sentence has suggested the next, but not one is on the topic. The most anxious watch must be kept in the selection of material. Some will be admitted without any question; some will be excluded with a brusqueness almost brutal. There is a third class, however, that is allied with the subject, yet it is not so easy to determine whether it should be admitted or rejected. This class requires the closest questioning. It must contribute to the strength of the essay, not to its pages, or it has no place there.

Scale of Treatment.

_There is another condition which must be considered in the selection of material, the scale of treatment._ If Macaulay had been asked by a daily paper to contribute a paragraph of five hundred words on Milton, he could not have introduced all the numerous topics which have their place in his essay of one hundred pages. He might have mentioned Milton's poetry and his character, the two main divisions of the present essay; but Dante and aeschylus, Puritan and Royalist, would scarcely have received notice. The second consideration in selecting material is the purpose and length of the essay, and the consequent thoroughness with which the subject is to be treated.

_The exhaustiveness with which an author treats any subject depends, first, on his knowledge._ Any person could write a paragraph on Milton; Macaulay and Lowell wrote delightful essays on the topic; David Masson has written volumes about him. These would have been impossible except to a person who had been a special student of the subject. Second, the thoroughness of the treatment depends _on the knowledge of the readers._ For persons acquainted with the record of the momentous events of Milton's time, it would have been quite unnecessary, it might be considered even an insult to intelligence, to go into such details of history. The shortest statement suffices when the reader is already familiar with the subject and needs only to know the application in this case. Third, the scale of treatment depends _on the purpose for which the essay is written._ If a newspaper paragraph, it is one thing; if for a magazine, it is quite another; if it is to be the final word on the subject, it may reach to volumes.