THE COLON
XXIV. The colon is used to indicate pauses more abrupt than those indicated by the semicolon.
God has willed it: submit in thankfulness.
The wind raged, and the rain beat against the window: it was a miserable day.
Nevertheless, you will say that there must be a difference between true poetry and true speech not poetical: what is the difference?
The first example contains two clauses that are connected in such a way as to justify us in putting them into one sentence; that it is God's will, is a reason for submitting. The proper point therefore should be something less than the full stop. But there is a striking difference between the clauses; for we pass from an affirmation to a command. Therefore something more than the semicolon is needed. Had the clauses been similar in construction, the pause would have been sufficiently indicated by the semicolon: "God has willed it; man has resisted."
In the second example there is not the same change of grammatical construction, but the change in thought is equally great; we pass from a statement of details to a statement of the general result. The colon is frequently used in sentences of this kind, where the phrase "in short" is implied but is not expressed.
Many writers indicate such abrupt changes by means of the dash.
XXV. A pause generally indicated by a semicolon may be indicated by a colon, when the semicolon is used in the sentence for pauses of a different nature.
The "Essay" plainly appears the fabric of a poet: what Bolingbroke supplied could be only the first principles; the order, illustration, and embellishments, must all be Pope's.