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Origin contested
“Mind your Ps and Qs”
What it means
Watch your behaviour; be careful what you do or say.
Where it comes from
Alehouses ran almost entirely on credit. The landlord chalked each customer’s pints and quarts on a slate behind the bar, to be settled on payday. Minding your Ps and Qs meant watching what you had run up.
How sure are we?
The tavern slate is the most frequently given origin. A rival account has printers’ apprentices confusing the lowercase p and q, which are mirror images in a type case. Both explanations are old, and neither can be shown to be original.