We know good for you is one way of saying "good job" or "well done." Who started using good on you instead?
On the LinkedIn Grammar Girl group, Jan S. asked, "Since when did 'Good ON you' instead of 'Good FOR you' become correct? I hear that constantly, and it grates on my nerves."
'Good on You' Comes from Australia
The New Partridge Dictionary of Slang says good on you is an Australian phrase dating back to 1907. Anecdotally, two Australian commenters on the LinkedIn page said that good on you is the standard phrase in that country, but one Australian dissenter said that although good on you is common, it is still viewed as slang.
The Concise English Dictionary labels good on you "Australian colloquial."
The Grammarphobia blog says good on you may have started in Australia, but it also could have started in Ireland.
What Does 'Good on You' Mean?
Anna Wierzbicka, of the Department of Linguistics at Australian National University, writes in Semantics, Culture, and Cognition: Universal Human Concepts in Culture-Specific Configurations that the phrase good on you is a working-class expression and reflects Australians' deep seated optimism. She says that although good on you is often interchangeable with congratulations or good job, it also has a different meaning: you may say good on you to a friend who has announced he will fight a difficult illness, for example—a situation in which congratulations or well done would be inappropriate. She concludes
Saying good on you, the speaker indicates that the addressee has displayed, in a conspicuous way, an attitude which the speaker assumes both she or he and the addressee admire. . . . in good on you, the stress is on people's potential, on what they can do, rather than on what they have done, and on the kind of person they have shown themselves to be.
Of course, good for you can be used the same way.
How Common Is 'Good on You'?
A Google Ngram search shows that good on you is used in both British and American books. The phrase begins its rise in popularity around 1960, and the scale shows that it is now more common in published American English than in published British English.
I fondly remember one of my American grade school teachers who used the phrase in the late 1970s. At the time, I thought goodonya was some kind of play on the word lasagna.
With good on you showing up in a slang dictionary and being labeled "colloquial" in a regular dictionary, it's fair to say that although the phrase is common, it hasn't quite made the leap to being considered Standard English.
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