<P> Another proposal concerns the use of Norman French in medieval England; as the English dialect of the 11th century had no qs, one must watch their usage in court or discourse with the French Norman conquerors . </P> <P> Quinion cites an apparently related expression of pee and kew for "highest quality" used in 17th - century English: "The Oxford English Dictionary has a citation from Rowlands' Knave of Harts of 1612: "Bring in a quart of Maligo, right true: And looke, you Rogue, that it be Pee and Kew ." Nobody is really sure what either P or Q stood for . To say they're the initials of "Prime Quality" seems to be folk etymology, because surely that would make "PQ" rather than "P and Q". </P>

Where does watch your p's and q's come from