If anyone tells you starting sentence with a coordinating conjunction (and, but, for, nor, or, so, yet) is incorrect, hand them any piece of professional writing and have them take a look. In literature, journalism, speeches, and formal writing of all kinds, using these conjunctions to start sentences is more than just acceptable; it’s ubiquitous. Open any book, even one with technical, scholarly, or otherwise formal writing, and you are likely to find numerous examples. There are exceptions, of course, but these are rare. That there is some sort of rule against sentence-beginning conjunctions is an old myth that never seems to go away despite the fact that it is not at all borne out in the writing of actual English speakers.
There are many reasons to start a sentence with a coordinating conjunction (as far as we know, nobody questions the use of subordinating and correlative conjunctions to start sentences). For instance, sometimes it helps create the tone of an afterthought or a second guess—e.g., “I think I’ll go to the store. Or maybe I’ll just stay home.” Sometimes it helps create a smoother transition between sentences—e.g., “If you don’t like conjunctions at the beginnings of sentences, then don’t use them. And if you don’t mind them, then don’t worry about it.” Sometimes it helps move an argument or narrative forward—e.g., “When he went to bed that night, he was human. So he was surprised to wake up the next morning with paws instead of hands.” Sometimes sentence-beginning conjunctions just sound right. Fluent English speakers need not question their instincts on this.
As with many longstanding English myths, there are people who feel strongly about this one. But there is no reason to appease these people in this case—except perhaps when they happen to be our teachers or bosses—as this myth is especially useless, and the sooner it’s forgotten, the better.
A few examples don’t prove anything—the proof in this case is all around us—but we’ll include some just for fun:
But if a man sitting still has not the power to remove himself, he is not at liberty. [John Locke]
And even Mary could assure her family that she had no disinclination for it. [Jane Austen]
Yet I love facts, and hate lubricity and people without perception. [Ralph Waldo Emerson]
So we had quite a long talk when you were looking at the ruins, and he told me all about his life, and his struggles, and how fearfully hard it had been. [Virginia Woolf]
And to seek to make the blacksmith a scholar is almost as silly as the more modern scheme of making the scholar a blacksmith. [W.E.B. Du Bois]
But before the captain could answer, a major appeared from behind the guns. [William Faulkner]
And let every other power know that this hemisphere intends to remain the master of its own house. [John F. Kennedy]
Or it might just be that people who are susceptible to mental illness are more prone to think about these sorts of things. [David Foster Wallace]
But the truth is, these steps won’t make up for the seven million jobs that we’ve lost over the last two years. [Barack Obama]