Links in this essay will take you to information about the usage experts and their work. Numbers in parentheses are page references in the sources.
A comma splice occurs when two independent clauses are joined with a comma but no coordinating conjunction (and, but, and so on) or with a comma and a conjunctive adverb (however, furthermore, and so on). All usage experts endorse the general rule outlawing comma splices; the only debate concerns which exceptions to the rule, if any, are allowable. Because comma splices are considered serious errors, the line between acceptable and unacceptable use is not always easy to draw.
Why are comma splices condemned as serious errors? First, they suggest that the writer lacks the ability to comprehend the boundaries of a sentence. Second, comma splices, especially those with a comma and a conjunctive adverb, can cause misreadings, as in the following passage quoted by Bryan Garner:
The remnants of Hurricane Opal will move north. . . . Winds near the center of the storm will diminish rapidly, however, wind gusts over 60 miles an hour will persist around the storm center. (724)
Readers at first think that however goes with the clause they have just read, but in fact it goes with the next clause. A semicolon before the conjunctive adverb howeverwould prevent such a misreading.
Comma splices caused by a missing coordinating conjunction get more leeway from usage experts. Many of them agree that in the hands of an experienced writer, a deliberate comma splice can be effective—but only if no possible misreading results.
William Strunk Jr. and E. B. White say that a comma splice is acceptable "when the clauses are very short and alike in form" (6–7), as in these examples:
Man proposes, God disposes.
The gates swung apart, the bridge fell, the portcullis was drawn up. (7)
When clauses are closely parallel, skilled writers sometimes use a comma splice even when the clauses are not so short, especially to draw a sharp contrast:
The pleasures of the intellect are permanent, the pleasures of the heart are transitory.
—Henry David Thoreau
Think like a man of action, act like a man of thought.
Bryan Garner, however, cautions all writers, regardless of their sophistication, to be careful. Even when a comma splice may be justified, he writes, "some readers are likely to object" (724). And Wilson Follett, while pointing out that some comma splices are "swift and emphatic," cautions inexperienced writers to "seek safety through semicolons, conjunctions, or separate sentences" (295-96).
Conclusion: When you use a comma splice deliberately—for effect—you are taking a risk. Only you can decide whether that risk is worth taking.
Source: Hacker Handbooks (Boston: Bedford, 2013).