[Fiji Hill]

"Mind your Ps and Qs": A warning to printers’ apprentices to take care when selecting the little blocks with letters on, to ensure that they didn’t confuse the P block with the Q block, and vice versa.

I had always thought that the phrase meant "mind your pints and quarts," meaning don't imbibe too much alcohol.

[BwanaNdege]

When you're filling the "stick" with all those lead letters to make up a printing block, the letters are all BACKWARDS.

"p" and "q" can easily be confused, as well as "b" and "d".

[impactplayer]

I agree - they told us when we visited Williams burg that this is what the wives told the men as they went out in the evening.

[firebrand]

Both the p and the q are easily confused with other letters. Not with each other.

[txnativegop]

professors who teach logic claim that mind your p’s and q’s comes from the their field. lol