coordinating conjunctions: starting a sentence with and or but

Standard English allows a sentence to begin with and, but, or another coordinating conjunction.

A coordinating conjunction (and, but, or, nor, for, so, or yet) joins elements of equal rank and does not subordinate the clause it introduces. An independent clause that opens with one therefore remains independent and forms a complete sentence: Yet the bridge held. A subordinating conjunction such as because or although subordinates an independent clause, so Although the bridge held cannot stand alone as a sentence.

Sentence-initial and appears in the ninth-century Old English Chronicle, and sentence-initial but dates at least to Middle English. The belief that a sentence may not open with either word is a myth that schoolroom teaching spread in the nineteenth and early twentieth centuries.

A coordinating conjunction that opens a sentence takes no comma after it: And the ferry sailed at dawn. When an introductory phrase or clause follows the coordinating conjunction, the comma goes after that phrase or clause: But once the storm passed, the ferry sailed at dawn. Setting off the phrase or clause as a parenthetical, with a pair of commas (But, once the storm passed, the ferry sailed at dawn), is not an error, but it gives the sentence a heavier, more old-fashioned feel.

Of the coordinating conjunctions, only nor needs care, because it puts an auxiliary verb before the subject: Nor had the mayor signed the order. When the clause after nor has no auxiliary, a form of be comes before the subject in the same way (Nor was the hall open), and any other verb takes do (Nor did the council object).

Examples

Use Laura phoned the bank twice. And both times she reached a recording. (No comma follows And.)

Use Marcus had rehearsed the toast for a week. But when he raised his glass, he forgot his first joke. (The comma follows the clause when he raised his glass, not But.)

Use Ana never answered the invitation. Nor did she explain her absence. (Nor puts did before the subject she.)

Avoid The museum is free on Sundays. But, the line stretches around the block. (The comma after But is incorrect, because a coordinating conjunction that opens a sentence takes no comma after it. Write The museum is free on Sundays. But the line stretches around the block.)