Commas

The comma indicates the smallest interruption in continuity of thought or sentence structure. Aside from a few obligatory rules, comma use is mainly a matter of good judgment, with ease of reading as the goal.

Use commas in these situations.

• After each item in a series of three or more with a single conjunction: This section addresses analysis, design, and implementation.
• Adverbial clauses or phrases: When management accepts the quote, you can send it to the customer.
• Adjectival clauses or phrases: This screen, which is a new enhancement, reduces duplication of data entry.
• Appositives: His wife, Elizabeth, had written to their congressman.
• Complementary or antithetical elements: This road leads away from, rather than toward, your destination.
• Compound sentences: Are we really interested in preserving law and order, or are we only interested in preserving our own privileges?
• Coordinate adjectives: It was a long, hot summer.
• Introductory participial phrases: Exhausted by the morning’s work, the writer napped in the cubicle.
• Mistaken junction: She recognized the man who entered the room, and fainted.
• Parenthetical elements: To say the least, the offer was late.
• Before quotations: Miriam said calmly, “I have no idea what you mean.”
• Separating identical or similar words: Whatever it is, is good.
• Titles, addresses, and dates:
  • The first speaker was Alex Jacklin, Product Documentation Manager.
  • Send all proofs to the writer at 150 Spear Street, San Francisco, California.
  • On December 14, 2009, the group attended the meeting.
• Enclose an expression, such as that is or namely, and the element it introduces in parentheses only if a comma doesn't signal a big enough break in continuity:
  • The task has been closed, that is, the Status field has a “Closed” value.
  • Users in a territory can be granted read, read/write, or owner-like access (that is, the ability to view, edit, transfer, and delete records) to the accounts in that territory.
• When parentheses or brackets enclose an independent sentence, place the period or comma inside. Otherwise, place the period or comma outside.
• For numbers with four or more digits, use commas between groups of three digits, for example, 1,000 emails per user.