"conventional wisdom"

[Baker, John]

It looks like Howells used it earlier.  From William Dean Howells, April Hopes 438 (1888; copyright 1887) (via Google Book Search):
 
<<He could not think her superfluous, and she was very good-natured.  She made little remarks full of conventional wisdom, and appealed to his judgment on several points as they drove along.>>
 
John Baker
 
 

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