compound predicates: comma use
Whether a comma separates two verbs or verb phrases that share one subject.
Use no comma between two predicates that share a subject and are joined by and, but, or, nor, or yet: The editor checked the citations and corrected the dates. The subject, the editor, governs both verbs, checked and corrected. The same rule holds with but: We ordered the replacement but received the wrong part.
A compound predicate differs from two independent clauses. In The editor checked the citations, and her assistant corrected the dates, each clause has its own subject and verb, so a comma comes before and.
Add a comma within a compound predicate only when the sentence would otherwise be misread: She recognized the man who entered the lobby, and waved. Without the comma, the reader takes entered the lobby and waved as describing the man. The comma shows that she is the one who waved.
When three or more predicates share a subject, separate them with commas, as in any list: The technician inspected the wiring, replaced the fuse, and tested the alarm.
See also comma; comma before a coordinating conjunction; commas in lists; Oxford comma (serial comma).
Examples
Use The tenant reported the leak and requested a repair. (The two predicates share the subject the tenant, so no comma comes before and.)
Avoid The tenant reported the leak, and requested a repair. (The two predicates share one subject, so the comma before and is unnecessary. Write The tenant reported the leak and requested a repair.)
Use The tenant reported the leak, and the manager arranged a repair. (Each clause has its own subject, so a comma comes before and.)
Use You can submit the application online or bring it to the office. (The two predicates share the subject you, so no comma comes before or.)