Don't is the standard contraction for do not. As a contraction for does not, don't first appeared in writing in the latter half of the 17th century, about the same time as the first written appearance of other contracted forms with not, like mayn't and can't. Don't remained the standard contraction for does not in both speech and writing through the 18th century. During the 19th century, under pressure from those who thought it illogical and who preferred doesn't in that use, don't for does not gradually became less frequent in writing but continued to be common in speech. Don't for does not still occurs in the informal speech and in the personal writing of many Americans, including the well educated, especially in the Midland and Southern dialects. It does not occur in edited writing or formal speech.

don't vs. doesn't

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