2. When so—that, so—as, rather—than, more—than, connect expressions, the comma is usually omitted; as, “Ingratitude never so thoroughly pierces the human heart as when it proceeds from those in whose behalf we have been guilty of transgression.”—Fielding.
When, however, the expressions themselves are divided into smaller parts by commas, or are unusually long, they should be separated by a comma; as,—
“So over-violent, or over-civil,
That every man with him was God or Devil.”—Dryden.
3. When two short expressions are united by as or than, a comma should not be used; as,—
“He knew what’s what, and that’s as high
As metaphysic wit can fly.”—Butler.
When, however, the expressions are long, it is better to use a comma; as, “I have no more pleasure in hearing a man attempting wit and failing, than in seeing a man trying to leap over a ditch and tumbling into it.”—Dr. Johnson.
4. When the first expression is negative and the other affirmative, a comma should be placed between the expressions and before the negative word, if it does not commence a sentence; as, “The world generally gives its admiration, not to the man who does what nobody else even attempts to do, but to the man who does best what multitudes do well.”—Macaulay.