know better

English

know better (third-person singular simple present knows better, present participle knowing better, simple past knew better, past participle known better)

(set phrase) To recognize that a statement or belief is false or doubtful.
- 1841 February–November, Charles Dickens, “Barnaby Rudge. Chapter 54.”, in Master Humphrey’s Clock, volume III, London: Chapman & Hall, […], →OCLC:
  'Do you think, sir,' said Mr Willet, […] 'do you think, sir, that I'm a born fool?'
  'No, no, Johnny,' returned Solomon, looking round upon the little circle of which he formed a part: 'We all know better than that.'
- 1987 April 24, Bruce Lambert, “Operator of Newsstands Guilty in Sales Tax Case”, in New York Times, retrieved 19 May 2015:
  "Kapoor Brothers told us they had no books or records, but we knew better and were able to search and find them."
(set phrase) To understand that certain behavior is wrongful, futile, or inappropriate.
- 1919, H. H. Munro, “Hyacinth”, in The Toys of Peace and Other Papers:
  "All that happened when he was eight; he's older now and knows better."
- 2010 March 8, Tony Karon, “Israelis and Palestinians: Agreeing to Talk, and to Fail”, in Time, retrieved 19 May 2015:
  [B]oth sides know better than to expect that U.S. special envoy Senator George Mitchell's shuttling between Jerusalem and Ramallah will be able to bridge the chasm between their demands.

Sometimes used without further explication and sometimes used with than followed by a description of the belief or behavior, as in "He knows better than to take what does not belong to him".
Know better has a much higher tendency to be used in the positive (example: "he knows better") than its synonym, know any better (example: "he didn't know any better").