There are likewise internal causes equally forcible. The language most likely to continue long without alteration, would be that of a nation raised a little, and but a little, above barbarity, secluded from strangers, and totally employed in procuring the conveniencies of life; either without books, or, like some of the Mahometan countries, with very few: men thus busied and unlearned, having only such words as common use requires, would, perhaps, long continue to express the same notions by the same signs. But no such constancy can be expected in a people polished by arts, and classed by subordination, where one part of the community is sustained and accommodated by the labour of the other. Those who have much leisure to think, will always be enlarging the stock of ideas; and every increase of knowledge, whether real or fancied, will produce new words, or combinations of words. When the mind is unchained from necessity, it will range after convenience; when it is left at large in the fields of speculation, it will shift opinions; as any custom is disused, the words that expressed it must perish with it; as any opinion grows popular, it will innovate speech in the same proportion as it alters practice.
As by the cultivation of various sciences, a language is amplified, it will be more furnished with words deflected from their original sense; the geometrician will talk of a "courtier's zenith, or the eccentrick virtue of a wild hero;" and the physician of "sanguine expectations and phlegmatick delays." Copiousness of speech will give opportunities to capricious choice, by which some words will be preferred, and others degraded; vicissitudes of fashion will enforce the use of new, or extend the signification of known terms. The tropes of poetry will make hourly encroachments, and the metaphorical will become the current sense: pronunciation will be varied by levity or ignorance, and the pen must at length comply with the tongue; illiterate writers will, at one time or other, by publick infatuation, rise into renown, who, not knowing the original import of words, will use them with colloquial licentiousness, confound distinction, and forget propriety. As politeness increases, some expressions will be considered as too gross and vulgar for the delicate, others as too formal and ceremonious for the gay and airy; new phrases are, therefore, adopted, which must, for the same reasons, be in time dismissed. Swift, in his petty treatise on the English language, allows that new words must sometimes be introduced, but proposes that none should be suffered to become obsolete. But what makes a word obsolete, more than general agreement to forbear it? and how shall it be continued, when it conveys an offensive idea, or recalled again into the mouths of mankind, when it has once become unfamiliar by disuse, and unpleasing by unfamiliarity?