contrasting phrases: comma use
The commas that set off a phrase that states a contrast, such as one beginning with not.
A comma precedes a contrasting phrase introduced by not: The flight leaves from Gate 12, not Gate 21. A contrasting phrase in the middle of a sentence takes a comma on each side: The interview is on Tuesday, not Wednesday, at ten o’clock.
A contrast built on not . . . but takes no comma, because the two parts form a single paired construction: The delay was caused not by the weather but by a broken signal.
See also comma; correlative conjunctions and parallelism; not only . . . but also; comma before a coordinating conjunction.
Examples
UseLinda ordered the salmon, not the steak. (A comma precedes a contrasting phrase introduced by not.)
UseThe concert starts at eight, not seven, on Saturday. (A contrasting phrase in the middle of a sentence takes a comma on each side.)
UseThe problem is not the price but the delivery time. (A contrast built on not . . . but takes no comma.)
AvoidThe tickets cost forty dollars not thirty. (A comma must follow dollars, because a comma precedes a contrasting phrase introduced by not. Write The tickets cost forty dollars, not thirty.)
AvoidThe game is on Friday, not Thursday at the high school. (A comma must follow Thursday, because a contrasting phrase in the middle of a sentence takes a comma on each side. Write The game is on Friday, not Thursday, at the high school.)