Of these two definitions obviously the first attempts merely to satisfy the intellectual curiosity of the reader, is a mere report of facts, and the second is interested in making an interpretation, in stimulating the reader. For most readers the words of Gissing would be more interesting; though, since a dictionary is not primarily an amusement, it is a bit unfair to mention the fact.
Interesting our expository writing must be; it must also be truthful. Nothing worse can be imagined than the kind of writing that forgets the facts, that remembers only the desire to please. Under the pleasing phraseology of any bit of expository writing there must be the firm structure of thought, and the close weave of fact. Expository writing is commonly divided into Definition and Analysis. Definition attempts to set bounds to the subject, to say "thus far and no farther," to tell what the subject is. Analysis regards the subject as composed of parts, mutually related, which together form the whole, and attempts to divide the subject into as many parts as it contains. Analysis is divided into classification and partition. Classification groups individual members according to likeness, as one might classify Americans according to color or birthplace or education or health, in every case placing those who are alike together. Partition divides an organic whole into its parts, as one might divide the United States Government into its three branches of legislative, judicial, and executive, or the character of George Washington into its components. Now definition and analysis often intermingle and help each other, and are often informally treated, but somehow, in every piece of exposition, the underlying thought must have a sound basis of one or the other or both. This will be the nucleus of the thinking; it may then be treated as a bald report or as an interpretation, aiming merely to give information or to rouse the further interest of the reader. The method of treatment will be determined by the nature of the facts and the purpose of the author in writing.
It cannot be too strongly stated that the underlying thought and the interest are really one, after all. As you approach a subject, and learn its character and meaning, you will be at the same time learning whether it is a subject capable of great appeal or only of slight attraction. Interest is not something laid on, but is a development from the nature of the facts themselves. The first question should be, "Is this interesting?" and then the second question may follow, "How shall I bring out the interest?" Remember that interest depends on relation to human beings; the closer the relation, the greater the interest.
Mr. Henry Labouchere, English statesman and for many years editor of Truth, had an ideal reaction to life, so far as interest is concerned. If, scanning the horizon for interest, he had bethought himself of the rather impolite advice of the Muse to Sir Philip Sidney, "'Fool,' said my Muse to me, 'look in thine heart and write,'" he would have found, upon following the advice, a heart full of eager curiosity and readiness to be attracted to anything. The following account of one of his qualities, as related in his biography, is worth remembering when you feel like saying, "Oh, I don't see anything interesting in that!": "If he had encountered a burglar in his house already loaded with valuables, his first impulse would have been, not to call the police, but to engage the intruder in conversation, and to learn from him something of the habits of burglars, the latest and most scientific methods of burgling, the average profits of the business, and so forth. He would have been delighted to assist his new acquaintance with suggestions for his future guidance in his profession, and to point out to him how he might have avoided the mistake which had on this occasion led to his being caught in the act. In all this he would not by any means have lost sight of his property; on the contrary, the whole force of his intellect would have been surreptitiously occupied with the problem of recovering it with the least amount of inconvenience to his friend and himself. He would have maneuvered to bring off a deal. If by sweet reasonableness he could have persuaded the burglar to give up the 'swag,' he would have been delighted to hand him a sovereign or two, cheer him with refreshment, shake hands, and wish him better luck next time; and he would have related the whole story in the next week's Truth with infinite humor and profound satisfaction."
To make clear, to explain,—that is the task of exposition. Such writing does not have the excitement of the fighting-ring, which we find in argument, nor does it attain the lyric quality of impassioned description, or the keen wild flight of narrative. It keeps its feet on the earth, tells the truth—but tells it in such a way, with so much of reaction on the writer's part, and with so strong an appeal to the reader's curiosity or imagination or sympathy, that it is interesting, that it is always adequate, and may be powerful.