B. Foundations of Language · Foundations: Grammar, Sentences and Punctuation

Commas for Essential and Non-Essential Information

B3.3 B3.1 B3.2About 45 minutes

Learning goals

I can tell essential (restrictive) information from non-essential (non-restrictive) information.
I can use commas to set off non-essential clauses and appositives, and leave them out for essential ones.
I can choose that or which and explain how commas change meaning.
I can use commas between coordinate adjectives and choose commas, dashes or parentheses for interrupters.

Words to know

essential (restrictive)
Information the sentence needs to identify which person or thing you mean. No commas.

non-essential (non-restrictive)
Extra information that could be removed without changing which person or thing you mean. Set off with commas.

appositive
A noun phrase that renames the noun beside it: my cousin Aisha; Mr. Ross, our coach,

coordinate adjectives
Two or more adjectives that each describe the noun equally: a long, cold winter.

interrupter
A word, phrase or clause that breaks into a sentence to add a comment: The trail, I think, is closed.

How many brothers?

My brother who lives in Calgary is a nurse.
My brother, who lives in Calgary, is a nurse.

Sentence 1 suggests I have more than one brother, and I mean the one in Calgary. The clause is essential: it tells you which brother.

Sentence 2 suggests I have one brother. Who lives in Calgary is just extra information, so it is set off with commas.

Two little commas tell the reader something big. That's why Grade 8 asks you to use punctuation to communicate meaning precisely.

No commas: the clause picks out one brother from several. Commas: there is only one brother, and the clause just adds a fact about him.

Remember from earlier grades

In Grade 5 you used commas with appositives and participial phrases. In Grade 6 you learned that extra (non-essential) adjective clauses take commas. In Grade 7 you used dashes for breaks. Now you'll decide on purpose, using a test.

The dashed yellow box is extra information: take it out and you still know which person is meant. The solid green box is essential: it tells which students.

The removal test

Cover the clause or phrase with your finger. Does the sentence still tell you which person or thing?

Yes → non-essential → use commas.
No → essential → no commas.

Students who finish early may read quietly. Cover who finish early: Students may read quietly. Now all students may read, which is not what the teacher meant. So it's essential: no commas.

That or which?

In Canadian writing, many style guides recommend:

that for essential clauses (no commas): The bike that has a flat tire is mine.
which for non-essential clauses (with commas): My bike, which is blue, has a flat tire.

Who works for people either way; the commas show the difference.

Appositives follow the same rule

My friend Amir plays the drums. (I have several friends; Amir tells which one.) No commas.
My best friend, Amir, plays the drums. (I have one best friend; his name is extra.) Commas on both sides.

Coordinate adjectives

Put a comma between adjectives if you could put and between them and switch their order.

a long, cold winter → a cold and long winter ✅ → comma.
a heavy winter coat → a winter and heavy coat ❌ → no comma.

Interrupters: commas, dashes or parentheses?

Commas are neutral: The trail, I think, is closed.
Dashes add emphasis: The trail — the only way down — is closed.
Parentheses make it quieter, like an aside: The trail (built in the 1970s) is closed.

Worked example

Let's decide on commas

Add commas if needed: (a) The CN Tower which is in Toronto attracts many visitors. (b) The tower that we climbed had 300 steps.

(a) Cover which is in Toronto. The CN Tower attracts many visitors. We still know which tower: there's only one CN Tower. Non-essential → commas.
(b) Cover that we climbed. The tower had 300 steps. Which tower? We don't know. Essential → no commas. (That also signals essential.)

(a) The CN Tower, which is in Toronto, attracts many visitors. (b) The tower that we climbed had 300 steps. (no commas)

Worked example

Let's explain a meaning change

Explain the difference: (a) The students who had permission forms went on the trip. (b) The students, who had permission forms, went on the trip.

(a) No commas → the clause is essential. It picks out some students: only those with forms went.
(b) Commas → the clause is extra. All the students went, and (by the way) they all had forms.

In (a) some students stayed behind; in (b) everyone went. The commas change who went on the trip.

Don't forget the second comma

A non-essential element in the middle of a sentence needs a comma on both sides: Ms. Patel, our principal, spoke first. Leaving out the second comma is one of the most common errors in Grade 8 writing.

Just for fun

What if commas went on strike? The dogs which were barking woke the baby would turn into a mystery: were all the dogs guilty, or just the noisy ones?

Hands-on activity

Comma meaning sketches

You need: paper and pencil crayons.

Fold a paper in half. On each side, write one sentence from this pair:

The dogs that were barking woke the baby.
The dogs, which were barking, woke the baby.

Draw a quick sketch that shows the meaning of each. (Left: several dogs, and only the barking ones are guilty. Right: all the dogs were barking.)
Make up two pairs of your own about your family or neighbourhood and sketch them too.
Show a family member the sketches without the sentences. Can they match each sketch to the right sentence?

What to look for: sketches show some (essential, no commas) versus all (non-essential, commas).

Your turn

Add commas if needed: Lake Superior which borders Ontario is the largest of the Great Lakes.

Add commas if needed: The book that I borrowed is overdue.

Add commas if needed: My grandmother who was born in Winnipeg loves curling. (I have two grandmothers.)

Add commas: Mr. Haddad our science teacher grew up in Halifax.

Choose that or which: The jacket ___ I wanted was sold out.

Comma or not? a bright sunny morning / a dark winter night

Rewrite with dashes to add emphasis: The prize, a trip to Ottawa, went to our class.

More practice: warm-up

Essential information gets commas: true or false?

Which word usually starts an essential clause: that or which?

How many commas does a non-essential phrase in the middle of a sentence need?

What is an appositive?

Which punctuation adds the most emphasis to an interrupter: commas, dashes or parentheses?

More practice: on your own

Add commas if needed and explain: Canada's capital which is Ottawa sits on the Ottawa River.

Explain the difference: (a) My cousin Leah is visiting. (b) My cousin, Leah, is visiting.

Fix the missing comma: Our coach, who never misses a practice is sick today.

Comma or not? a crisp clear autumn day

Combine with a non-essential clause: The Rideau Canal is in Ottawa. It becomes a skating rink in winter.

Challenge

Write two sentences about teachers, one with an essential clause and one with a non-essential clause, and explain the difference in meaning.

A sign says: Students, who are late, must sign in at the office. What does the sign accidentally say? Fix it.

Punctuate: Nunavut which became a territory in 1999 has its capital in Iqaluit a city on Baffin Island.

Check your understanding

Quiz

Which sentence means all the players were tired?

Which sentence is punctuated correctly?

Which word best fits? The pencil ___ I lent you is my favourite.

Which needs a comma between the adjectives?

What is wrong with Ms. Diaz, our coach is from Sudbury?

Which punctuation makes an interrupter sound like a quiet aside?

For parents and teachers

What this lesson is about: using commas to show whether information is essential (identifying) or extra, including clauses, appositives, coordinate adjectives and interrupters. It is a meaning skill, not just a punctuation rule.

How to help at home:

Use the removal test aloud: "If we cover this part, do we still know which one?"
Look for examples in news articles, where non-essential clauses are common (the mayor, who was elected last year, said...).

Common difficulties:

Missing the second comma after a mid-sentence non-essential element.
Putting commas around essential clauses because the sentence "feels long".
That vs. which: some published writers use which for essential clauses too. Students should know the common recommendation and, most importantly, the comma rule.