Can you use a comma at one end and a dash at the other?

No. An insertion is fenced with the same mark at both ends: two commas or two dashes. A comma at one end and a dash at the other is half a fence, and so is a mark at one end only. If one end is already printed, copy it.

How do I know if a phrase needs commas around it?

Lift it out and read what is left. If the sentence still stands and still means much the same, the phrase is extra information and takes a fence. If the reader would no longer know which one is meant, the phrase is needed and takes no marks.

Do I put commas around a clause that begins with that?

Not usually. A clause that begins with that tells the reader which one you mean, so it cannot be lifted out. It takes no marks, and nothing separates a subject from its verb, however long the subject is.

Do I put commas around a name after a noun, like the sculptor Nell Brandt?

It depends on whether the name says which one. If there are several sculptors and the name tells you which, it cannot be lifted out and takes no commas. If the noun already points to one person, the name is extra information and takes a comma on each side.

Is there a difference between commas and dashes for extra information?

Both fence off the lifted words, and either works as long as the two ends match. A question that offered both pairs for the same words would have two right answers, so the choices differ in the matching, not in your preference.

Commas and dashes around extra information

Words that could be lifted out of a sentence are fenced at both ends with the same mark: two commas or two dashes, never one of each, and never only one. Words that say which one is meant cannot be lifted out and take no marks at all.

1.Lift out the words in question and read what is left. If it is still a complete sentence that means much the same, the words were extra information.
2.Fence extra information at both ends with the same mark: two commas or two dashes. Never one of each, and never a mark at only one end.
3.One end of the fence is usually printed in the passage. Find it, then put the same mark at the blank.
4.If lifting the words out leaves the reader unsure which one is meant, they are not extra. They say which one, and they take no marks at all.

Try it on a question

Work it below before you open the working. The steps say what to do, and you can do each one yourself.

Mrs Tanner grows most of the food for her household on a long strip of land behind her cottage. Her greenhouse, which stands at the bottom of the ______ is heated by a small wood stove from October until the last frost. She grows tomatoes in it from the first week of March.

Which choice completes the text so that it conforms to the conventions of Standard English?

Choice A: garden —
Choice B: garden;
Choice C: garden,
Choice D: garden

1
Read the sentence and find the words that could be lifted out. Say which end of them the slot is at: the start or the finish.
2
Find the other end of the fence in the sentence. It is already printed. Then try each mark at the slot and read the verdict.
3
Notice the sentence where nothing is right. If the words tell you which one is meant, lifting them out would leave the reader guessing, so they take no marks at all.

Fences come in pairs

Sentence 1 of 5

Words that could be lifted out are fenced at both ends, with the same mark at each.

The ferry, which crosses the estuary twice a day the slot carries more bicycles than cars.

1. Cover one side, then the other. Can each stand alone as a sentence?

Left of the slot

“The ferry, which crosses the estuary twice a day”

Right of the slot

“carries more bicycles than cars.”

2. Try the marks. Which are legal here?

Answer for both sides first.

The full working, and why each wrong choice is there

Lift out "which stands at the bottom of the garden" and the sentence still stands: "Her greenhouse is heated by a small wood stove from October until the last frost." So the words are extra information, and they are fenced at both ends with the same mark. A comma opened the fence after greenhouse, so a comma closes it.

Choice A: garden —
A dash can fence off an insertion, so it looks respectable. But the other end of this one is a comma, and the two ends of a fence match.
Choice B: garden;
A semicolon marks a longer pause than a comma, which can make it feel like the careful choice. It needs a complete sentence on each side, and the words before it are only the start of one.
Choice C: garden,the answer
Lift out which stands at the bottom of the garden and the sentence still stands. A comma opened the insertion after greenhouse, so a comma closes it.
Choice D: garden
Without a mark here, nothing shows where the extra information stops, and the sentence never picks up again.

Use it when

A choice puts a comma or a dash at one end of a group of words, and the other end of the group already has a mark printed.
A phrase beginning with which, or a name or description that renames the noun before it, sits in the middle of a sentence.
The choices differ only in a comma, a dash, a semicolon or no mark at one spot, and the sentence has not finished.

Do not use it when

The choices differ in a verb, a pronoun or a different word, not in a mark. This move settles punctuation and nothing else.
Two complete sentences meet at the blank. That is a question about joining sentences, and a matching mark is not what decides it.
The words after the noun begin with that, or name the one that is meant. They cannot be lifted out, so no fence goes round them.

Five questions on this move

Untimed, and nothing is saved. A wrong first answer gets one more try before the working is shown.

Question 1 of 5

The old signal ______ built from local brick in 1911 — stands beside the track at the edge of the village. Nobody has worked in it since the line closed. The parish council hopes to turn it into a small museum of railway tools.

Which choice completes the text so that it conforms to the conventions of Standard English?

Five is a start

In your account there is a focused set of ten on Boundaries from the question bank, with the same one more try. And after each practice test, the drills your plan sets for the skills you missed name the moves for them.

Practise Boundaries in your account

How this page was checked

Every punctuation answer, by our rule table
For each of the 6 questions on this page, what stands on each side of the blank is recorded, and an automated test checks that our table of punctuation rules calls the keyed choice legal and the other three not.
The whole page, by a person
Not yet. Every question and every item of its lab was worked through in a browser by Claude, an AI assistant, on 14 October 2026. The page was published on 14 October 2026 before a person had read it. If something here is wrong, tell us and it is put right.

The questions were drafted with AI and are original: none is a College Board question, and none comes from the question bank behind our practice tests.

Where this comes from

“Matching fences” is one card from the Preptics lesson Boundaries: name the job before you pick the mark, which sits under the Digital SAT skill Boundaries. The lesson has the other cards around it, and its questions come back for review on a schedule. The lessons are part of the Digital SAT track.

Common questions

Can you use a comma at one end and a dash at the other?: No. An insertion is fenced with the same mark at both ends: two commas or two dashes. A comma at one end and a dash at the other is half a fence, and so is a mark at one end only. If one end is already printed, copy it.
How do I know if a phrase needs commas around it?: Lift it out and read what is left. If the sentence still stands and still means much the same, the phrase is extra information and takes a fence. If the reader would no longer know which one is meant, the phrase is needed and takes no marks.
Do I put commas around a clause that begins with that?: Not usually. A clause that begins with that tells the reader which one you mean, so it cannot be lifted out. It takes no marks, and nothing separates a subject from its verb, however long the subject is.
Do I put commas around a name after a noun, like the sculptor Nell Brandt?: It depends on whether the name says which one. If there are several sculptors and the name tells you which, it cannot be lifted out and takes no commas. If the noun already points to one person, the name is extra information and takes a comma on each side.
Is there a difference between commas and dashes for extra information?: Both fence off the lifted words, and either works as long as the two ends match. A question that offered both pairs for the same words would have two right answers, so the choices differ in the matching, not in your preference.

Keep going

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