Consider these two sentences: (A) 'The student who studies hardest usually wins.' (B) 'My sister, who lives in Paris, called last night.' Why does sentence A have no commas around the relative clause while sentence B does?
AThe clause in A is shorter, so it doesn't need commas; longer clauses require them
B'Who studies hardest' is essential to identify which student, while 'who lives in Paris' is nonessential bonus information about a person already fully identified
CSentence A uses present tense and sentence B uses past tense, which triggers different comma rules
DA comma is optional in both sentences; it depends on the writer's style guide
This is the essential/nonessential distinction. In sentence A, removing 'who studies hardest' changes the meaning entirely — you'd be saying all students win, not the hardest-working one. The clause is essential for identifying which student, so no commas. In sentence B, removing 'who lives in Paris' leaves 'My sister called last night' — the full meaning is preserved because the speaker has only one sister. The clause is nonessential bonus information, signaled by commas. The commas here carry real semantic weight, not just punctuation style.
Question 2 Multiple Choice
Which sentence correctly applies the comma rule for two independent clauses joined by a coordinating conjunction?
AShe studied hard, but, she still failed.
BShe studied hard but she still failed.
CShe studied hard, but she still failed.
DShe studied hard but, she still failed.
When two complete, independent clauses (each with its own subject and verb) are joined by a coordinating conjunction (FANBOYS: for, and, nor, but, or, yet, so), a comma goes before the conjunction. 'She studied hard' and 'she still failed' are each complete sentences, so 'but' gets a comma before it: 'She studied hard, but she still failed.' Option B has no comma at all. Options A and D place the comma incorrectly — after the conjunction or in both positions.
Question 3 True / False
'In the morning, the frost had melted' correctly uses a comma after the introductory phrase to mark where the main clause begins.
TTrue
FFalse
Answer: True
'In the morning' is an introductory prepositional phrase that comes before the main subject ('the frost') and verb ('had melted'). The comma after it marks the boundary between the introductory material and the main clause. Without it, readers might briefly misparse 'In the morning the frost' as a noun phrase. This is the first comma rule: introductory material — whether a single word, short phrase, or dependent clause — is separated from the main clause by a comma.
Question 4 True / False
A comma should generally be placed before 'and' in a sentence, so 'She bought apples and oranges' should be written 'She bought apples, and oranges.'
TTrue
FFalse
Answer: False
A comma before 'and' is only required in two situations: (1) in a series of three or more items (e.g., 'apples, oranges, and bananas') — where the Oxford comma before the final 'and' is the debated option; and (2) when 'and' joins two independent clauses. With only two items in a series ('apples and oranges'), no comma is needed. Adding one here is an overcorrection based on the misconception that 'and' always requires a comma.
Question 5 Short Answer
Explain why the commas in 'My brother, who lives in Denver, called last night' are not merely decorative. What meaning do they signal, and what would change if you removed them?
Think about your answer, then reveal below.
Model answer: The commas signal that 'who lives in Denver' is nonessential — it provides additional information about a person already fully identified (the speaker has one brother and doesn't need the clause to specify which one). Removing the commas would convert the clause to essential, implying the speaker has multiple brothers and is using 'who lives in Denver' to identify which one called. The presence or absence of commas changes whether the clause is understood as defining or merely describing.
This is the most consequential comma rule because it actually changes meaning, not just readability. 'My brother who lives in Denver called' (no commas) implies other brothers exist. 'My brother, who lives in Denver, called' (with commas) implies one brother who happens to live in Denver. The comma is doing semantic work: it is marking the parenthetical status of the clause. Misplacing or omitting these commas can genuinely mislead readers.