ACT® · English: Punctuation Conventions
Correcting Misused Colons and Semicolons
A colon can only follow a complete sentence, but what comes after it can be a list, a phrase, or another clause. A semicolon must have a complete sentence on both sides, so it can never introduce a list.
Colons and semicolons look like cousins because both can sit between two clauses, but they have different jobs. A colon works like an announcement: it says 'here comes the explanation' or 'here's the list I promised.' The rule is strict on one side only. Everything before the colon must be able to stand alone as a complete sentence, with a subject and a full verb phrase. Everything after it is flexible. It can be a single word, a list, a phrase, or even a full sentence.
A semicolon is stricter in both directions. It glues two complete sentences together, so you have to be able to test each side independently. Cover the semicolon and read the left chunk alone. Cover it again and read the right chunk alone. If either side fails to stand as its own sentence, the semicolon is wrong. This is exactly why a semicolon can't introduce a list: 'She packed; a rope, a torch, and matches' fails because 'a rope, a torch, and matches' isn't a sentence.
This test matters most where writers reach for a colon or semicolon right after a verb, thinking any pause deserves punctuation. 'The kit includes: a rope...' fails because 'the kit includes' isn't complete without its object. Strip the colon and the sentence reads fine on its own, which is the giveaway. This connects to the rest of punctuation work on the page: colons and semicolons both police the boundary between complete and incomplete clauses, just with different rules for what's allowed afterward.
Key terms
- colon
- A mark that follows a complete sentence and introduces a list, explanation, or example.
- semicolon
- A mark that joins two complete sentences, each of which could stand alone as its own sentence.
- independent clause
- A group of words with a subject and a full verb that can stand alone as a complete sentence.
- left-side test
- Reading only the words before a colon or semicolon to check whether they form a complete sentence.
Watch it explained
- How it worksHow does a colon require a complete sentence in front of it while allowing anything after it?
- How it worksWalk me through testing the left side of any colon or semicolon for a full standing sentence.
- Worked exampleFind the punctuation error in 'She had one goal; to finish before dark.' and correct it.
- Common mistakeWhy isn't a semicolon usable in front of a list the way a colon is?
Check yourself
End of topic.