Doesn’t is a contraction of does not and should be used only with a singular subject. Don’t is a contraction of do not and should be used only with a plural subject. The exception to this rule appears in the case of the first person and second person pronouns I and you. With these pronouns, the contraction don’t should be used. He doesn’t like it. They don’t like it.
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Grammar Tip: Don’t & Doesn’t. They Don’t Mix
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