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From the Chicago Manual of Style: There is a widespread belief—one with no historical or grammatical foundation—that it is an error to begin a sentence with a conjunction such as 'and', 'but', ...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/26418 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
From the Chicago Manual of Style: > There is a widespread belief—one with no historical or grammatical foundation—that it is an error to begin a sentence with a conjunction such as 'and', 'but', or 'so'. In fact, a substantial percentage (often as many as 10 percent) of the sentences in first-rate writing begin with conjunctions. It has been so for centuries, and even the most conservative grammarians have followed this practice. But only do this for emphasis. And not all the time. So it doesn't get old.