A parenthetical phrase adds a comment or extra detail to a sentence. For example: “My neighbor, an excellent baker, brought me cookies.” The phrase an excellent baker describes a neighbor already understood from context. Remove it and the main statement remains: “My neighbor brought me cookies.” Commas, parentheses or dashes can mark the addition.
Use the examples to compare punctuation and meaning, then try seven questions and an editing task. The answers stay closed until you choose to check them. Your browser’s print command gives you the practice with space to write.
Parenthetical examples: words, phrases and clauses
The wider term parenthetical expression includes more than phrases. Compare a word, a phrase and a clause:
- Word: The results, surprisingly, were better than expected. The word comments on the result.
- Noun phrase: Mr. Harrison, my history teacher, gave us a surprise quiz today. The phrase gives another description of the named person; it is an appositive.
- Prepositional phrase: The project, after many delays, was finally completed. The phrase is presented as an interruption.
- Clause: The old house, which had been empty for years, was finally sold. The addition has a subject and verb, so it is a clause.
For the basic distinction between restrictive and additional information, see Purdue OWL’s nonessential-elements guidance. The examples here are practice sentences, not reports of personal or classroom experience.
Commas, parentheses and dashes
Often more than one punctuation choice is grammatical. Choose the effect you intend and keep the boundaries of an interruption clear.
Commas: a closely connected addition
“The dog, a golden retriever, wagged its tail excitedly.” Paired commas mark the description as extra information. The sentence continues after the addition, so both commas are needed.
“We visited the Eiffel Tower, a famous landmark in Paris.” Here the addition ends with the sentence, so the full stop completes it; no closing comma is needed.
Parentheses: a separate aside
“Please fill out the form (available at the front desk) before your appointment.” Parentheses, also called round brackets, keep the note separate. They do not automatically make a sentence formal.
“The final score was 3–2 (a very close game).” The full stop belongs to the whole sentence and follows the closing parenthesis. Both parentheses are still needed at sentence end.
Dashes: a more noticeable interruption
“My new hobby—collecting vintage board games—is surprisingly expensive.” The pair of em dashes gives the inserted detail more emphasis. The sentence resumes with is surprisingly expensive.
“There is only one thing I want for my birthday—a new puppy.” One dash can introduce an addition at the end. A hyphen, as in solar-powered, has a different job.
The Purdue OWL punctuation overview explains parentheses and dashes; its guide to emphasis compares their force with commas. Cambridge’s punctuation guide also shows that punctuation includes conventions and choices, not just one fixed answer.
Repair an unfinished interruption
“The manager, who was very busy left the meeting early” needs a second comma after busy when the clause is additional information. Likewise, use a matching pair in “My new phone—an impressive model—is also waterproof.” Commas or parentheses could enclose that phone description instead.
Essential or additional? Check the context
Removing an expression may leave a grammatical sentence while changing which person or thing you mean. Ask whether the words identify the subject or add information about one already identified. Compare these two valid sentences:
- You must identify one student among several: “The student who aced the final exam will receive an award.” The clause selects the student. No commas enclose it.
- You are already discussing a particular student: “The student, who aced the final exam, will receive an award.” The clause adds a fact about that student. It does not mean only one student exists.
The same contrast can appear with relatives: “My oldest brother, who is a doctor, lives in Chicago” adds information about the already identified oldest brother. “My brother who is a doctor lives in Chicago” can identify the doctor among several brothers. Neither punctuation pattern is wrong without knowing the intended reference.
Keep both checks: does the remaining sentence work, and does it still identify the intended person or group? For more on clauses that identify a noun, continue to the clause guide and practice.
Exercise 1: Identify the parenthetical expression
For each sentence, write the added expression and then the sentence without it. In question 2, also decide whether the addition is a phrase or a clause. Treat the described people and things as already identified.
- My cousin, a skilled mechanic, fixed my car’s engine.
- The movie—which lasted nearly three hours—was incredibly boring.
- The final report (due on Friday) is almost complete.
- Our dog, a scruffy but lovable terrier mix, loves to play fetch.
Check questions 1–4: expressions and explanations
- a skilled mechanic. Remaining sentence: “My cousin fixed my car’s engine.” The noun phrase describes the cousin already being discussed; it is not selecting a cousin from a group here.
- which lasted nearly three hours. Remaining sentence: “The movie was incredibly boring.” This is a clause: which is its subject and lasted its verb. It is parenthetical, but not a phrase in the narrower grammatical sense.
- due on Friday. Remaining sentence: “The final report is almost complete.” The phrase adds the deadline; it does not identify a different report in this context.
- a scruffy but lovable terrier mix. Remaining sentence: “Our dog loves to play fetch.” This noun phrase describes the dog. The two commas enclose the whole addition, including but lovable.
Exercise 2: Add punctuation for a stated effect
Keep all the words. Follow the requested style, then explain another grammatical choice and how it would change the emphasis.
- Use commas to present a yearly tradition as additional information about an already identified festival:
The local festival a yearly tradition was cancelled due to bad weather. - Use a pair of dashes to draw attention to the description:
His newest invention a solar-powered can opener was a complete failure. - Use parentheses to make a fact I learned yesterday a separate aside:
The scientific name for a lion is Panthera leo a fact I learned yesterday.
Check questions 5–7: models and valid alternatives
- The local festival, a yearly tradition, was cancelled due to bad weather. The main clause resumes with was, so close the addition after tradition. Parentheses would separate the note more; dashes would emphasize it. Those are grammatical alternatives, although this prompt asks for commas.
- His newest invention—a solar-powered can opener—was a complete failure. The second dash ends the interruption before was. Commas or parentheses are possible if you want less emphasis. Keep the hyphen in solar-powered; it joins words within the description.
- The scientific name for a lion is Panthera leo (a fact I learned yesterday). Close the parentheses before the sentence’s full stop. A comma or a single dash before a fact would also introduce the end addition, with a more connected or more emphatic effect. The aside describes when the speaker learned the fact; it is not an academic citation.
Editing task: Preserve the intended meaning
In each context, add commas only where the intended meaning needs them. Then write one sentence explaining who receives an invitation. Do not change the words.
A. Selecting a group: A workshop has 20 applicants. Only eight submitted a portfolio; only those eight receive an invitation.
The applicants who submitted a portfolio will receive an invitation.
B. Adding a fact: A second workshop has six applicants. All six submitted a portfolio, and all six receive an invitation. The writer presents the portfolio submission as an additional fact about the entire group.
The applicants who submitted a portfolio will receive an invitation.
Check the editing task: two contexts, two readings
A: “The applicants who submitted a portfolio will receive an invitation.” Keep it without commas: the clause identifies the eight applicants who qualify, excluding the other twelve.
B: “The applicants, who submitted a portfolio, will receive an invitation.” The commas present the submission as additional information about all six applicants.
A version without commas in B could still describe the same six people, because all six happen to meet the condition. It would present the clause as identifying the qualifying group instead of making the requested aside. Explain that distinction rather than treating every different punctuation choice as a grammatical error. Deleting the clause from A changes which group the sentence refers to, even though the remaining sentence is grammatical.
Choose your next writing check
- To separate phrases from clauses, use the clause examples and exercises.
- To check whether your main sentence is complete, review sentence structure.
- For a wider self-check, try mixed grammar questions with explained answers.
Frequently asked questions
Can a parenthetical expression be one word?
Yes. In The results, surprisingly, were better than expected, surprisingly is a one-word comment. Parenthetical expressions can be words, phrases or clauses; not every example is a phrase in the grammatical sense.
Does a sentence that still makes sense after removal prove the information is nonessential?
No. You must also check which person or thing the sentence identifies. Removing who aced the final exam can leave a grammatical sentence while changing which student the writer means. Context determines whether the clause identifies the student or adds information about a student already identified.
Can I print the practice without the answer key?
Yes. Use the browser print command for the seven questions and the editing task with writing space. Answer explanations, model responses and reference sections are hidden in print. Open the answer sections on screen to check your work.
Sources and editorial note
Prepared by The Kingdom of English with AI-assisted drafting and source checks, updated October 21, 2026. The Purdue OWL and Cambridge references are linked beside the explanations. This revision retains useful examples and seven practice stems, adds explained answers, and introduces an original workshop editing task. The public material is separate from the platform’s assignment library. See our editorial approach; report a correction with its question number through our public contact route.