You have probably been told at one point in your writing life some hard and fast rules about grammar. One popular rule handed down through generations is: "Never start a sentence with "but."
The word "but" is a popular conjunction found in many sentences.
What are conjunctions?
Conjunctions are words that join words and groups of words. There are three different kinds, of conjunctions: subordinating, correlative and coordinating conjunctions. AKA: F.A.N.B.O.Y.S. (for, and, nor, but, yet, so). Since conjunctions are generally used to connect two or more things, appearing at the beginning of the sentence breaks away from its original purpose.
But good writing often breaks rules, and style and voice require rhythm. There's something about a formally constructed sentence that can suck the life out of prose.
Grammar rules were intended to serve the writer—no writer should be burdened by them.
So...
Can you start a sentence with "but"?
Yes! If the sentence requires the natural rhythm of casual conversation or if the writer wants to emphasize the impact of a sentence by setting it apart from its related clause, yes.
If the writer likes the sound of the sentence better that way—absolutely.
Here's one example :
"Then he said this was the first time he had ever done something like this. But we all knew better." If you put the two sentence together without the full stop, the second half of the thought would lose its impact.
Can you start a sentence with "and"?
Yes! "And" is a popular coordinating conjunction that joins words or groups of words, but it can also begin a sentence.
"And just then it occurred to him he was going to die." -Ernest Hemingway
He could have written: "He looked longingly out the window, and just then it occurred to him he was going to die." He would have written a perfectly parallel, correctly punctuated compound sentence, but it would be longer, slower, and weaker.
Hemingway was the king of the strong declarative sentence. He often began with a conjunction. Shorter sentences maintain a faster pace.
Note: If you begin a sentence with "but" or "and" don't place a comma after it. You won't need it.
Purpose and audience matter
If you want your writing to be clean, clear, and concise, grammar rules are extremely helpful. But if you want to create dynamic sentences or more creative or casual ones, break the rules if it improves the rhythm. After you're sure the idea of your sentence is clear, ask yourself, "how do I want the reader to hear this sentence?"
This is where style comes in.