So let’s say you see these answers choices on the SAT writing section…
A) NO CHANGE
First, you know you are being tested on transition words. That also could mean you are being tested on run-on sentences, which go hand-in-hand with fragments.
Some students mistakenly would eliminate B and C, believing that if two transition words are the same then both are wrong.
But remember that parts of speech matter.
“However” is an adverb, specifically, a conjunctive adverb. It cannot join two independent clauses with a comma alone.
WRONG: “He was tired, however, he finished the race.”
CORRECT: “He was tired; however, he finished the race.” or “He was tired. However, he finished the race.”
“But” is a coordinating conjunction; it can join two independent clauses, with a comma.
CORRECT: “He was tired, but he finished the race.”
Here’s how to recognize those sneaky conjunctive adverbs such as “however.” If you can move a transition word around the sentence, it is likely a conjunctive adverb.
Indeed, “however” can be moved around. “However,” indeed, can be moved around. “However,” can indeed be moved around. “However” can be moved around indeed. Like “indeed,” “instead,” “therefore,” and many other conjunctive adverbs, “however” can be moved around; it is, therefore, a conjunctive adverb. Therefore, it cannot join independent clauses with a comma.
Correct: I was tired; however, I finished the race.
Correct: I was tired. However, I finished the race.
Correct: I was tired; I did, however, finish the race.
Correct: I was tired; I did finish the race, however.
By the way, with the word “but,” a period is technically acceptable, as “but” is a coordinating conjunction, meaning it creates two independent clauses. CORRECT: “I was tired. But I finished the race.” Do a page-search (control-f”) for the text “. But” on most New York Times articles to find numerous sentences that have “But” as the first word.
It’s a perfectly acceptly way to begin a sentence, but on the SAT you’ll likely see a comma for coordinating conjunctions such as “but.”