Bob the Brit

To mind your Ps and Qs means to be polite and to mind your manners.

The origin of this phrase is unclear, there are several possible explanations, all equally plausible:

• inexperienced printers, back in the days of letterpress and movable type, would have to be particularly careful when selecting the letters p and q as they look very similar, and the reverse letters required for printing are even more confusing
• children, on being taught politeness would be encouraged to remember their ‘pleases and thank yous’
• inns and taverns would often run bar tabs for customers (often chalked on a piece of slate – hence ‘putting it on the slate’) – these bar tabs would comprise a list of p’s – representing pints or q’s representing quarts. As a quart contains two pints, the difference could be substantial, so bar staff would be encouraged to mind their p’s and q’s.