Mind your Ps and Qs

Mind your Ps and Qs is an English language expression meaning "mind your manners", "mind your language", "be on your best behaviour", "watch what you're doing".

Look up mind one's ps and qs in Wiktionary, the free dictionary.

Attempts at explaining the origin of the phrase go back to the mid-19th century. One explanation favoured in a letter to the editors of Notes and Queries dated 1851, is a literal interpretation of the saying, regarding the lowercase letters p and q in the context of the school-room or typesetting in the printing-office.[1] This is given as a common suggestion by the 2007 revision (3rd edition) of the Oxford English Dictionary, but the OED considers the explanation unlikely since "the chronology of the senses would argue against this, and no such connotation is evident in the earliest quotations" and says that the origin of the expression is unknown.[2]

Movable type could be missorted if you're not paying attention.

According to Michael Quinion, "[i]nvestigations by the Oxford English Dictionary in 2007 when revising the entry turned up early examples of the use of Ps and Qs to mean learning the alphabet. The first is in a poem by Charles Churchill, published in 1763: ‘On all occasions next the chair / He stands for service of the Mayor, / And to instruct him how to use / His As and Bs, and Ps and Qs.’ The conclusion must be that this is the true origin."[3]

When pupils were taught to write lowercase alphabet, the positioning of the vertical line before or after the circle represented different letters: d & b, p & q. Pupils also had to mind the placement of the letters when writing the alphabet eg. p comes before q. As noted by W. D. Henkle in Educational Notes and Queries in 1876, in this case the proper spelling of the phrase should be "note your p's and q's", because the distinction of majuscule P and Q does not pose a problem.[4]

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Nevertheless, a number of alternative explanations have been considered as more or less plausible. Another explanation suggests that "Ps and Qs" is short for "pleases" and "thank-yous", the latter of which contains a sound similar to the pronunciation of the name of the letter "Q". Another proposed origin is from the English pubs and taverns of the 17th century. Bartenders would keep a watch on the alcohol consumption of the patrons; keeping an eye on the pints and quarts that were consumed. As a reminder to the patrons, the bartender would recommend they "mind their Ps and Qs".[5] This may also have been a reminder to bartenders not to confuse the two units, written as "p" and "q" on the tally slate.[3]

Other origin stories, some considered "fanciful",[3] could come from French instructions to mind one's pieds (feet) and queues (wigs) while dancing. However, there is no French translation for this expression.[6] Another origin could be from sailors in the 18th century who were reminded to pay attention to their peas (pea coat) and queues (pony tail).[6]

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. [7]

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”.[3]