Commas

While a period ends a sentence, a comma indicates a brief pause.

Use a comma

• Before the conjunction in a list of three or more items. This is known as the Oxford Comma.
• Following an introductory phrase.
• In a series of two or more adjectives that precede a noun when their order is interchangeable.
• To separate conjunctive adverbs (in addition, also, on the other hand, however, moreover, furthermore, for example, finally).

Here is a full list of conjunctive adverbs:

Don't use a comma

• To join independent clauses when you don't use a conjunction. Use a semicolon instead.
• Between two verbs that apply to the same subject.
• Between the month and the year when a specific date isn't mentioned.