Comma usage is one of the most complex, and most misunderstood, questions of proper punctuation. In some cases there are widely accepted rules governing comma usage; in a few cases, there is more than one acceptable approach. Students often think it’s silly to worry about things such as punctuation: after all, isn’t the legal analysis what really counts? However, when one applies for a job or submits written work to a supervisor, nothing will leave a more negative impression than ignorance of the basic rules of punctuation.

• When you begin a sentence with a phrase or dependent clause to introduce a subsequent independent clause, separate the clauses with a comma.
• Use commas to set off a nonrestrictive clause in the middle of a sentence, but not to set off a restrictive clause.
• Use two commas to set off an appositive or an aside in the midst of a sentence.
• Use two commas, not one, to set off a nonrestrictive clause in the middle of a sentence.
• Place a comma after a transitional word that introduces a sentence.
• When using commas to separate items in a list, place a comma before the conjunction that precedes the last separate item in the list, unless that last item is a compound term.
• Use a comma to separate two adjectives that modify the same noun, but do not use a comma if the first of two adjectives modifies the second adjective, but not the noun.
• Do not use a comma to replace the word “that.”
• Do not use a comma to separate the parts of a double predicate, unless the sentence would be confusing without it, or the second part of the double predicate requires special emphasis.
• When joining two independent clauses with a conjunction, place a comma before the conjunction. Conjunctions include the words “and,” “but,” “or,” “nor,” and “yet.”
• Generally, use a comma before “which” but not before “that.”
• Place commas inside, not outside, quotation marks.
• Use two commas when setting off dates and places.