Colon Acts like a Period
Many writers use the colon between two independent clauses, especially when the subject matter of the second clause expands on, or exemplifies, the subject matter of the first. Some writers start the second clause with a capital letter; others use lowercase.
Richard Cohen Example
In the May 17, 2001, edition of The Washington Post, columnist Richard Cohen uses a colon to separate two independent clauses. (In the passage, please note how Mr. Cohen uses parallel structure: He creates four present-participial phrases to begin the first sentence.)
Having been condemned to death for mass murder at Oklahoma City, having confessed to the crime, having waived all appeals, having chosen Gore Vidal to turn his death into literature, McVeigh now sees his execution delayed almost a month on account of a procedure pimple: The FBI, with characteristic efficiency, misplaced some 3,000 documents relating to the case. Richard Cohen, Delayed Martyrdom, The Washington Post, May 15, 2001, p. A17.
Michael Kinsley Example
In the June 22, 2001, edition of The Washington Post, columnist Michael Kinsley uses a colon to separate two independent clauses and begins the second with a capital letter. (Please note that he also starts the sentence with the conjunction But.)
But an equally dyspeptic conservative might say that's just the point: For a generation now, politicians have clamored to be called conservative without dismantling any significant aspect of big government. Michael Kinsley, Liberalism à la Mode, The Washington Post, June 22, 2001, p. A25.
[The colon] may link two separate clauses or phrases by indicating a step forward from the first to the second: the step may be from an introduction to a main theme, from a cause to an effect, from a general statement to a particular instance, or from a premise to a conclusion. Garner Oxford, pp. 68-69.
But the other view—urging for a lowercase word following the colon—is probably sounder: the lowercase (as in this very sentence) more closely ties the two clauses together. Although the uppercase convention is a signpost to the reader that a complete clause is ahead, that signpost generally isn't needed. Garner Oxford, p. 69.
Strunk & White’s Approach
Strunk & White also uses a lowercase letter to begin an independent clause following a colon. Though the work doesn't expressly say so, the example shows the correctness of the lowercase letter:
But even so, there was a directness and dispatch about animal burial: there was no stopover in the undertaker's foul parlor, no wreath or spray. Strunk & White, p. 8.
In my writing, I opt for uppercase, for I think it does alert the readers to an upcoming complete sentence and in that way aids and hastens their reading. But you can't go wrong using lowercase.
The important point, of course, is this: You should recognize this use of the colon and weave it into your writing style. Good writers routinely use complete sentences to follow colons. You should, too. Pick either uppercase or lowercase. For either is correct.
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