1
general::
Phrase(s): Two wrongs do not make a right.
Prov. Someone else may do something bad and not be punished, but that does not mean you are allowed to do bad things. • Jill: I’d really like to humiliate Fred, after he made fun of me in front of everyone at lunch. Jane: Now, now, Jill. Two wrongs don’t make a right.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
A second misdeed or mistake does not cancel the first, as in Don't take his ball just because he took yours? two wrongs do not make a right. This proverbial adage sounds ancient but was first recorded in 1783, as Three wrongs will not make one right.
American Heritage Idioms