1. Relative clauses are generally introduced by the relative pronouns who, which, that, or what.
2. A comma should be placed before the relative clause, even when it is necessary to complete the meaning of the antecedent,—
a. When the relative is immediately followed by a word or an expression inclosed in commas; as, “As a man, he may not have deserved the admiration which he received from those, who, bewitched by his fascinating society, worshiped him nightly in his favorite temple at Button’s.”—Macaulay.
b. When the relative has several antecedents that are separated from each other by commas; as, “All those arts, rarities, and inventions, which vulgar minds gaze at, the ingenious pursue, and all admire, are but the relics of an intellect defaced with sin and time.”—South.
3. The words of which are sometimes preceded by a comma, even when they are necessary to complete the meaning of the antecedent: as, “His mind was formed of those firm materials, of which nature formerly hammered out the Stoic, and upon which the sorrows of no man living could make an impression.”—Fielding.
Rule IV. Parenthetical Words and Phrases. When single words and phrases break the connection between closely related parts of a sentence, they should usually be separated by commas from the rest of the sentence.
1. Words used parenthetically,—
- therefore,
- indeed,
- perhaps,
- namely,
- finally,
- consequently,
- however,
- moreover,
- nevertheless, &c.
2. Phrases used parenthetically,—
- in short,
- in truth,
- of course,
- in fact,
- in a word,
- you know,
- in reality,
- no doubt,
- as it were, &c.