ACT® · English: Punctuation Conventions
Deleting Commas in Compound Subjects and Compound Verbs
A comma before 'and' is only earned when a complete second sentence follows. If 'and' just joins two subjects or two verbs sharing one clause, no comma belongs there.
Every comma before 'and' makes a promise: a full second clause, with its own subject and verb, is coming. 'The pilot checked the gauges, and radioed the tower' breaks that promise. 'Radioed the tower' has no subject of its own, it is just a second verb sharing 'the pilot' with 'checked.' One subject, two verbs, joined by plain 'and' - no comma. The same logic runs in reverse for compound subjects: 'Rainfall in April, and snowmelt in May filled the reservoir' has one verb, 'filled', shared by two subjects, 'Rainfall' and 'snowmelt.' Since the verb only shows up once, the two halves before it are one subject, not two clauses, so the comma splitting them has to go.
The test for whether a comma is earned is mechanical: cover up everything before 'and' and everything after it, and ask if what follows 'and' can stand alone as a sentence. In 'She wrote the grant application and she won the award,' 'she won the award' has its own subject and verb and works alone, so the comma before 'and' is correct. In 'She checked the gauges and radioed the tower,' 'radioed the tower' fails that test, so no comma.
This sits next to the larger punctuation unit because the same move - deleting an unearned comma - shows up with interrupters and modifiers too. The guiding question is always the same: does this mark sit at a real joint between two independent clauses, or is it just breaking one clause into pieces that were never separate?
Key terms
- Compound subject
- Two or more nouns sharing a single verb in one clause, such as 'Rainfall and snowmelt filled the reservoir.'
- Compound verb
- Two or more verbs sharing a single subject in one clause, such as 'The pilot checked and radioed.'
- Independent clause
- A group of words with its own subject and verb that can stand alone as a complete sentence.
- Unearned comma
- A comma placed where no grammatical joint, like a second independent clause, actually exists.
Watch it explained
- How it worksHow does a comma before 'and' promise a full second clause rather than just a second verb?
- Worked exampleFind the comma to delete in 'Rainfall in April, and snowmelt in May filled the reservoir.'
- Worked exampleWalk me through deciding whether the 'and' in 'She wrote the grant and she won it' needs a comma.
- Common mistakeWhy isn't every 'and' inside a long sentence a place where a comma belongs?
Check yourself
End of topic.