ACT® · English: Punctuation Conventions
Choosing Among Comma, Semicolon, Colon, and Dash
Comma, semicolon, colon, and dash can all sit between two parts of a sentence, but the choice depends on whether each half can stand alone and whether the second half explains or delivers on the first.
A semicolon and a period both need a complete sentence on each side, because a semicolon just marks a closer relationship between two statements than a period does. A colon and a dash also want a complete sentence on the left, but they announce that something is coming: an explanation, a result, a list, a punchline. The comma is the odd one out. It can join a complete sentence to a fragment, or link items in a series, but it can't join two complete sentences by itself. So the four marks aren't interchangeable flavors of the same move. Each one makes a different promise about what the two sides are doing.
The fastest way to choose is to test each half on its own. Can the first part stand as a complete sentence? Can the second? If both can, you're choosing among period, semicolon, colon, and dash based on relationship: semicolon for a close logical link, colon for 'here's what I mean' or 'here's the result,' dash for a sharper, more dramatic version of the same thing. If only the first half stands alone and the second is a list, a comma usually introduces it, unless the first half is a complete sentence setting up the list, which opens the door to a colon or dash instead. If the first half isn't even a complete sentence, by itself, no mark stronger than a comma belongs there, and sometimes no mark at all.
This is the same stand-alone test used to sort independent clauses from dependent ones and from phrases. Once that skill is solid, punctuation choice stops being about memorizing rules for each mark and becomes one consistent habit: check both sides, then match the relationship to the mark.
Key terms
- Independent clause
- A group of words with a subject and verb that can stand alone as a complete sentence.
- Colon
- A mark placed after a complete sentence to introduce an explanation, result, or list.
- Dash
- A mark that can join a complete sentence to what follows with extra emphasis, similar to a colon but more dramatic.
- Stand-alone test
- Checking whether each half of a sentence could work as its own complete sentence.
Watch it explained
- How it worksHow does asking what each half can do on its own narrow four punctuation marks down to one?
- Worked exampleWalk me through choosing a mark for 'The results were clear the drug did nothing at all.'
- Common mistakeWhy isn't the most sophisticated-looking mark ever the reason to pick it on a test?
- Going furtherWhat changes about that choice when the second half is a list rather than a full clause?
- Ties togetherHow does picking a punctuation joint use the same stand-alone test that sorts clause types apart?
Check yourself
End of topic.