Although I’m not certain what the source was, I created this handy-dandy little checklist for comma usage early on in my writing career. I still use it from time to time, although more a gentle reminder than as a check_list. I hope you will find it useful too.

Comma usage blog

As an aid in using this checklist, I’m also including definitions of some of the terms used above. No offense implied should you already be familiar.

Restrictive and non-restrictive clauses: An adjective clause is restrictive when it limits the thing it refers to and is therefore essential to the sentence. Example: The store accepted returns that were less than sixty days old. If an adjective clause adds non-essential or extra information it is non-restrictive and should use a comma followed by which to introduce it. Example: Julia’s scarf, which was purchased three months ago, was not accepted as a return.

Introductory dependent clause: A group of words including a verb and a subject but does not express a complete thought and cannot stand alone, which introduces a sentence. Example: When I worry, I eat.

Example of non-restrictive clause in the middle of a sentence: The book, which was on the table, was on fire.

Appositive: A noun or noun phrase that renames another noun right beside it. Example: His hat, a billycock, was askew. His girlfriend, a short girl with flaming red hair, sat down beside him.

Parentheticals: A parenthetical is a statement or reference that is incidental and could be properly enclosed within parentheses (hence the name). Example: Parentheticals, for example, require commas.

Transitionals: Words and phrases used to connect one idea with the next. Example: The fingertips contain numerous nerve endings. To illustrate, pick up that branding iron.

Conjunction: A word used to connect clauses or sentences or to coordinate words in the same clause. Example: In his pocket he had a coin, a ring, and a piece of twine.

Independent clause: A clause (group of words consisting of at least a noun and a verb) that can stand alone as a simple sentence. Example: His car started smoothly and he took off for home.