Some basic comma guidelines
This is a quick wrap-up of the most common uses for commas. It’s not likely to be of much help to you if you’re just starting out. But if you’ve already studied commas, and most particularly if you’re familiar already with some of the grammatical terms commonly used in discussions like these, this list makes for a useful reminder.
Use commas
Within sentences, use commas . . .
To set off —
Most introductory words or phrases
All introductory clauses
Interjections
Items of direct address
Expressions of contrast
Nonrestrictive phrases or clauses
Parenthetical expressions (“sentence interrupters”)
To separate —
Coordinate adjectives
Items in a series (words, phrases, or clauses) of three or more
Words that would otherwise be misread
In place of omitted or understood words in parallel constructions
Before a tag question
Between sentences, use a comma . . .
To separate two independent clauses only when the comma precedes a coordinating conjunction
To separate three short, closely related independent clauses as a deliberate mark of style
Note that with an interrupter the issue is not whether it’s restrictive or nonrestrictive, but rather how closely related to the syntax of the sentence. The main sentence, with this word or phrase removed, should still make sense.
Don’t use commas
Within sentences, don’t use commas . . .
To join two independent clauses —
In place of a coordinating conjunction
In place of a semicolon or colon
Before a conjunctive adverb
To separate a subject and verb or verb and complement
To set off restrictive phrases or clauses
To set off compound elements, unless for special effect
. . .
clause: A string of words that has both a subject and a conjugated verb.
conjugated verb: A verb that shows time, like write, wrote, am writing, have written. The opposite of a conjugated verb is a form like to write or (on its own) writing or (on its own) written.
conjunctive adverb: A word like accordingly, consequently, however, therefore, meanwhile. These words are not conjunctions. They cannot link two independent clauses preceded only by a comma. (That would make for a comma splice.)
coordinate adjectives: Adjectives of equal importance, generally directly preceding the noun they modify. Rule of thumb: If you can place and between two adjectives without the result sounding odd, those are coordinate adjectives. (And so, yes, you use a comma between them.)
coordinating conjunction: and, but, or/nor, for, yet, so. A conjunction conjoins two like elements: two words, two phrases of whatever type, two dependent clauses, two independent clauses.
dependent clause: A clause that cannot “stand alone” as a sentence. Most typically, a clause beginning with a class of words that turns any independent clause into a dependent one (words like after, although, as, because) or a wh-word like who, which, or that that modifies (makes reference to) a noun.
independent clause: A clause that can stand alone as a sentence. A clause (so, a string of words having both a subject and a conjugated verb) that does not begin with the kind of word that indicates a dependent clause.
Examples:
I finished a first draft = independent clause
After I finished a first draft = dependent clause
Because I finished a first draft = dependent clause
When I finished a first draft = dependent clause
which I finished this week = dependent clause (used following the noun or noun phrase to which it applies, for example “the first draft”)