OBSERVATIONS.
OBS. 1.—Of pure interjections but few are admitted into books. Unimpassioned writings reject this part of speech altogether. As words or sounds of this kind serve rather to indicate feeling than to express thought, they seldom have any definable signification. Their use also is so variable, that there can be no very accurate classification of them. Some significant words, perhaps more properly belonging to other classes, are sometimes ranked with interjections, when uttered with emotion and in an unconnected manner; as, strange! prodigious! indeed! Wells says, "Other parts of speech, used by way of exclamation, are properly regarded as interjections; as, hark! surprising! mercy!"—School Gram., 1846, p. 110. This is an evident absurdity; because it directly confounds the classes which it speaks of as being different. Nor is it right to say, "Other parts of speech are frequently used to perform the office of interjections."—Wells, 1850, p. 120.
OBS. 2.—The word interjection comes to us from the Latin name interjectio, the root of which is the verb interjicio, to throw between, to interject. Interjections are so called because they are usually thrown in between the parts of discourse, without any syntactical connexion with other words. Dr. Lowth, in his haste, happened to describe them as a kind of natural sounds "thrown in between the parts of a sentence;" and this strange blunder has been copied into almost every definition that has been given of the Interjection since. See Murray's Grammar and others. Webster's Dictionary defines it as, "A word thrown in between words connected in construction;" but of all the parts of speech none are less frequently found in this situation.
OBS. 3.—The following is a fair sample of "Smith's New Grammar,"—i.e., of "English Grammar on the Productive System,"—a new effort of quackery to scarf up with cobwebs the eyes of common sense: "Q. When I exclaim, 'Oh! I have ruined my friend,' 'Alas! I fear for life,' which words here appear to be thrown in between the sentences, to express passion or feeling? Ans. Oh! Alas! Q. What does interjection mean? Ans. Thrown between. Q. What name, then, shall we give such words as oh! alas! &c.? Ans. INTERJECTIONS. Q. What, then, are interjections? Ans. Interjections are words thrown in between the parts of sentences, to express the passions or sudden feelings of the speaker. Q. How may an interjection generally be known? Ans. By its taking an exclamation point after it: [as,] 'Oh! I have alienated my friend.'"—R. C. Smith's New Gram., p. 39. Of the interjection, this author gives, in his examples for parsing, fifteen other instances; but nothing can be more obvious, than that not more than one of the whole fifteen stands either "between sentences" or between the parts of any sentence! (See New Gram., pp. 40 and 96.) Can he be a competent grammarian, who does not know the meaning of between; or who, knowing it, misapplies so very plain a word?
OBS. 4.—The Interjection, which is idly claimed by sundry writers to have been the first of words at the origin of language, is now very constantly set down, among the parts of speech, as the last of the series. But, for the name of this the last of the ten sorts of words, some of our grammarians have adopted the term exclamation. Of the old and usual term interjection, a recent writer justly says, "This name is preferable to that of exclamation, for some exclamations are not interjections, and some interjections are not exclamations."—GIBBS: Fowler's E. Gram., §333.