Origin of "All Is Fair in Love and War"

The earliest known origin of the sentiment "all is fair in love in war" is found in poet John Lyly's novel "Euphues: The Anatomy of Wit," published in 1579. The novel recounts the romantic adventures of a wealthy and attractive young man, and includes the quote "the rules of fair play do not apply in love and war." The first know appearance of the quote worded "all is fair in love and war" is in English author Francis Edward Smedley's 1850 novel "Frank Fairleigh" about the life of a schoolboy.

All's fair in love and war means there is no act that is too terrible or too great when you are going after the person you love or making war on your enemies. Usually the quote is uttered when someone is trying to justify bad behavior. While a case can be made that true love is worth any price, or whatever you have to do to win your war is necessary if your cause is just, a case can also be made to the contrary.