The cat sat on the mat after the party.
The cat sat on the mat, after the party.
I'd say there's a profound difference in meaning.
> The cat sat on the mat after the party.
The rule is that this doesn't require a comma because it comes at the end. Optional comma, if you move it to the front.
The rule is that this doesn't require a comma because it comes at the end. Optional comma, if you move it to the front.
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