When can a writer start a sentence with the word “but”?
My answer is anytime “but” is appropriate, and so long as it’s not overused. You see, “but” is a very versatile word that can serve in any of five ways—as a conjunction, a preposition, an adverb, a pronoun, and even a noun.
For instance, you can start a short-story with a “but” functioning as a preposition in the sense of “except,” as in this example:
“But for a tiny little smudge in the hem, Cynthia’s dress was spotlessly clean. No one would have thought that it came from the jet of blood from her unfaithful lover’s temple after she shot him pointblank…”
A dialogue can also start with “but” if need be, as in the following example where it’s used in the sense of “isn’t it that”:
“But you told me you loved only me,” Fred’s girlfriend reprimanded him the other night. “So who’s this girl you were seen kissing at the park last Sunday?”
“Calm down, Karen,” he replied. “That girl was Nona, a first cousin of mine that I hadn’t seen for years.”
Those two usages of “but” are, of course, distinct from that in the following sentence where “but” serves as a conjunction in the sense of “notwithstanding”:
“We invited him but he declined our invitation.”
In this case, it’s obvious that the “but”-clause can’t be positioned up front.
