Section 7: Some Comma Rules
Punctuation is the use of conventional (and agreed-upon) marks to guide readers through our written text. As writers, a primary goal should always be to guide our readers through the text as effectively and efficiently as possible. While this ability includes a range of higher-order considerations, proper punctuation can also help to guide readers by slowing them down, or speeding them up, or focusing them on a particular passage, or highlighting a key point, or indicating when one idea is complete and another is beginning. Previously, we discussed some common rules for punctuation, now we want to offer some thoughts on using commas more effectively.
Where Commas Might Be A Matter of Style or Convention
Case 1 - Commas in a series of adjectives modifying a single noun phrase:
Example: Although it is made of thin, delicate strands, a spider's web is not easily broken.
The Chicago Manual of Style refers to these as coordinate adjectives, and says they are "traditionally separated by commas," but that in the "open" style, the commas are often omitted. So according to Chicago, this comma is OPTIONAL.
The MLA Handbook says this comma is REQUIRED, unless the first adjective is modifyiing a unit:
This is a common research technique. (research technique is acting as a unit).
Case 2 - Commas in a series before a final coordinating conjunction.
Example: This sweater comes in three colors: slate, aqua, and burgundy.
The MLA Handbook and the Chicago Manual of Style agree that the final comma before the and is REQUIRED.
The AP Stylebook, on the other hand, would omit it:
I ordered a burger, fries and a coke.
Do you want vanilla, chocolate or strawberry ice cream?
Case 1 is a matter of style: the good writer can choose whether the comma interrupts the flow or offers a necessary pause. Case 2 is a matter of convention: the responsible writer will learn the convention used in her particular context.
Other resources:
Where Commas Are Absolutely Incorrect
Case 1 - Never put a comma between mandatory sentence constituents of the 5 basic clause types.
Example: The cat, jumped when the firecracker exploded.
NEVER between a subject and a verb
Example: The car, is in the shop.
NEVER between a linking verb and complement
Example: We expect, that we will see you tomorrow.
NEVER between a transitive verb and object
Case 2 - Never put a single comma between any two elements that are necessary constituents of a phrase or clause.
Example: Decked out with a host of sensors and cameras that, can detect what is around the vehicle, self-driving cars can operate without anyone behind the wheel.
NEVER between the relative pronoun and the rest of the relative clause.
Example: Jane was not totally happy with, her new cell phone.
NEVER between a preposition and its object.
Case 3 - Commas may, however, come in pairs when they are setting off a non-restrictive element or conjunctive adverb anywhere in the sentence.
To extend this point, all dependent clauses can be classified as restrictive or nonrestrictive.
- A restrictive clause gives essential information.
- Restrictive clauses are not put in commas.
- A nonrestrictive clause provides additional – but non-essential – information.
- Nonrestrictive clauses are often set apart from the rest of the sentence by a comma (if it's at the beginning or end of a sentence) or a pair of commas (if it's in the middle of a sentence).