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Good for you, you're saying the right thing, as in You've decided to enter the contest? Now you're talking! [Mid-1800s]
American Heritage Idioms
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Phrase(s): Now you’re talking!
Inf. Now you are saying the right things. • Tom: I won’t put up with her behavior any longer. I’ll tell her exactly what I think of it. Bill: Now you’re talking! • John: When I get back to school, I’m going to study harder than ever. Mother: Now you’re talking!
McGrawhill's American Idioms And Phrasal Verbs