The comma is the most regularly abused punctuation mark in written communication. Why? Well, apparently many people are under the impression that a comma is needed whenever they take a breath while reading a sentence aloud. There are certain rules, however, governing usage of the comma, and unless a writer can justify inserting a comma based upon one of these rules, then he or she should apply the unwritten rule: When in doubt, leave it out.
Why Does Comma Placement Matter?
Where a writer inserts a comma can completely change the meaning of a sentence. For example, there is a noticeable difference between saying, “When lightning struck the five cats, all fled the room;” and saying, “When lightning struck, the five cats all fled the room;” or between saying, “He invariably throws darts to the left and then dashes for a touchdown,” compared to saying, “He invariably throws, darts to the left, and then dashes for a touchdown.
The Rules of Comma Usage:
1. Use a comma to indicate a significant pause (the key word here is significant).
- Then, Tom fainted.
2. Use a comma before a coordinating conjunction (for, and, nor, but, or, yet, so) when it connects two independent clauses.
- Tom said he’d mow the lawn later, so he wouldn’t miss the game.
3. Use a comma after a subordinate clause when it begins a sentence. When a dependent clause comes at the end of a sentence, however, no comma is usually necessary.
- While I mowed the lawn, Tom watched the game.
4. Use commas to set off adjective clauses if they are not essential to the meaning of the sentence.
- Tom, whom I met in grad school, is the laziest person I know.
5. Use a comma or commas to set off conjunctive adverbs and phrases like however, for example, on the other hand, nevertheless, moreover, particularly, especially, therefore, and consequently — unless they are linking two independent clauses.
- Men are naturally lazy, however, and Tom is no exception.
- I agree I should not have married Tom; however, at the time, I was young and stupid.
6. Use a comma or commas to set off an appositive (word, phrase, or clause used as a noun that identifies or explains another noun or pronoun).
- Those were the best years of my life, the years before I met Tom.
- One of Tom’s coworkers, John Smith, has 15 cats but is allergic to them.
7. Use commas between items in a series (three or more words, phrases, or clauses).
- At the store, Tom purchased beer, potato chips, and pretzels.
- Tom likes to watch television, read mystery novels, and play golf.
- Tom went swimming, Tom lay in the sun, and then Tom fell asleep.
8. Use a comma or commas with direct quotations.
- Tom said, “I want you to marry me.”
- “I want you to marry me,” said Tom.
- “I want you to marry me,” Tom said, “so please say you will.”
9. Use a comma or commas to set off items in dates and addresses, but not ZIP codes.
- Tom was born Monday, March 12, 1985, in Winston Salem, North Carolina.
- Tom’s current address is Apt. B, 190 Browning Street, Jacksonville, Florida 89001.
10. Use a comma after an introductory phrase if the comma makes the meaning of the sentence clearer.
- After eating, Tom and Dave plopped back down in front of the television.
- In the early hours of dawn, I lie in bed and rue the day I met Tom.
11. Use a comma or commas to set off words, phrases, or clauses if they clearly break the flow of the sentence.
- Tom, please turn off that television and repair the dishwasher.
- Tom’s Uncle Frank, who chews tobacco, is coming for a visit next week.
- Tom lied about repairing the dishwasher, not that I expected him to tell the truth.
Exceptions to the Rules:
Although there are rules governing comma usage, even the most seasoned of writers will occasionally break one of these rules; however, when they do so, it is not because they pause to take a breath while reading a sentence aloud but because they have a valid reason for inserting a comma; for example, “To err is human; to forgive, divine” (Alexander Pope, An Essay on Criticism, 1711).
