Q: I have been struggling of late with the ideology of commas and conjunctions. Here is a quote from an MSN article: “There have been instances in the past where the Pakistanis arrested extremists after terrorist attacks on India but released them several months later, after the international pressure eased up.” I would have placed a comma before the clause beginning with “but.”
A: In some cases, comma use is governed by taste and rhythm, not by any formal rule of punctuation. And there’s no rule that a clause introduced with a conjunction must be preceded by a comma.
I don’t think that passage from the MSN article requires an additional comma. However, an author with somewhat different tastes in comma use might have placed the comma differently, like so:
“There have been instances in the past where the Pakistanis arrested extremists after terrorist attacks on India, but released them several months later after the international pressure eased up.”
And someone with your tastes in the matter would have used two commas: “There have been instances in the past where the Pakistanis arrested extremists after terrorist attacks on India, but released them several months later, after the international pressure eased up.”
Now here’s an author with a completely different take on commas. This passage, from John Updike’s Rabbit, Run, is quoted in my book Words Fail Me (pp. 89-90): Just listen as the protagonist, Rabbit Angstrom, shoots a basket on a playground, watched by a group of schoolboys:
“As they stare hushed he sights squinting through blue clouds of weed smoke, a suddenly dark silhouette like a smokestack against the afternoon spring sky, setting his feet with care, wiggling the ball with nervousness in front of his chest, one widespread white hand on top of the ball and the other underneath, jiggling it patiently to get some adjustment in air itself. The cuticle moons on his fingernails are big. Then the ball seems to ride up the right lapel of his coat and comes off his shoulder as his knees dip down, and it appears the ball will miss because though he shot from an angle the ball is not going toward the backboard. It was not aimed there. It drops into the circle of the rim, whipping the net with a ladylike whisper.”
Updike uses (and doesn’t use) commas here because of a rhythmic effect he’s employing to build suspense. It would be a crime to interrupt and separate some of those breathless clauses.
Nonfiction is different, of course. But when no rules are being broken, writers have a lot of latitude in comma use.