"Mind your Ps and Qs" means "be careful to behave well and avoid giving offense.
" The NOAD reports that its origin is unknown; it would refer to the care a young student must take in differentiating the tailed letters p and q .
english.stackexchange.com/users/252/kiamlaluno
I've always heard that it was originally short for "Mind your Pints and Quarts!"
Something an innkeeper (or what-have-you) would shout to an unruly common room to settle them down.
According to AUE no one's particularly sure, but they list a few other theories, including what they consider to be the most likely: "Mind your 'please's and 'thank you's".
Link: http://alt-usage-english.org/excerpts/fxmindyo.html
english.stackexchange.com/users/23/kitukwfyer
It means Be on your best behaviour; be careful of your language.
The date of the coinage of 'mind your Ps and Qs' is uncertain.
There is a citation from Thomas Dekker's play, The Untrussing of the Humorous Poet, 1602, which appears to be the earliest use of the expression: http://www.phrases.org.uk/meanings/mind-your-ps-and-qs.html
english.stackexchange.com/users/2303/Robusto
I read somewhere that it came about, ages ago, to remind people in the printing business, to be careful when typesetting 'p' and 'q', because it was easy to confuse the two.
In general, this would mean to take extra care with what you were doing.
Now, it appears to have several meanings including: Mind what you say Mind
your manners, specifically' pleases ' and 'thank yous' Mind your own business All of which are related.
I wonder if it would be acceptable to use 'mind your Ps and Qs' to mean take extra care with what you are doing ?
I have never heard the phrase used in that context.
english.stackexchange.com/users/3733/Sky Red
Anyone who has worked as a printer's devil knows the answer to the origin (and meaning) of the elderly term, "Mind your p's and q's."
I must preface my remarks on the origin of the term with brief background.
First.
The origin of the printing process using moveable type around mid 16th century was made possible by using individual molded glyphs that were the mirror-image of the desired printed image.
The nature of each individual glyph is that similarity exists among several different ones; notably, the p, q, d, and b.
The difference is the orientation of the glyph.
As it turns out, tiny letter decorations called serifs make telling one character from the other easier.
The sole exceptions are the p and q.
Their only different characteristic is that one is reversed—the mirror of the other.
Second.
Each different letter used is kept sorted in a multi-compartment drawer referred to as a type "case" organized by frequency-of-use.
Thus, "e" and "t" are near the centre of the case and less-frequently used letters such as "v" and "j" are near the sides.
This is done for speedy and correct page composition.
In use, the typesetter composes a document letter-by-letter, line-by-line to fill a page.
After the page is printed, the type block is cleaned, removed from the "chase," taken apart line-by-line, letter-by-letter and distributed back into the proper compartment in the type case for re-use.
Majuscules (capital letters) go in one case and minuscules (small letters) into another placed slightly below the other.
All this is done completely in reverse by a skilled apprentice referred to as "a printer's devil."
Most all this can be accomplished simply if not easily "by feel" until you run into the two most-easily confused glyphs where you must pay special attention to keep them correctly sorted by heeding the admonition to " Mind your p's and q's ."
english.stackexchange.com/users/51153/Stan
There are many theories, (some of them given in answers here) but none of them has any supporting evidence
whatever.
WorldWideWords has an article.
english.stackexchange.com/users/547/Colin Fine
It's to do with the fact that children often confuse the small 'p' with the small 'q' when learning how to write and read (like they do with b's and d's.)
So if taken literally it is basically an appeal to 'be careful, be precise, listen to what you teacher has told you' - which comes pretty close to its use in language (i.e. mothers with their children.)
english.stackexchange.com/users/6869/Chuck
Another theory I have heard - probably apocryphal - is that it has to do with the two branches of the Celtic family of languages: P-celtic (i.e. Brythonic - Welsh etc.) and Q-celtic (i.e. Goideilic - Irish etc.).
It was said to date from when these were beginning to separate and you had to get the pronunciation right in each area to be understood.
To be honest this sounds rather unlikely as why would it be an idiom in English - a language from a completely different family.
english.stackexchange.com/users/4335/neil
I've always understood as a warning to be polite.
And I've always seen it this way: Mind
your P's and Q's as in your "Pleases" (P's) and "Thank-yous"(Q's), thus the origin of P's and Q's...
I don't know if anyone else has the same notion?
english.stackexchange.com/users/8183/Thursagen
During office discussion two turns of phrase came up in close proximity: "peace and quiet" shortly followed by "mind your P's and Q's".  What is the meaning of P's and Q's?  I wondered if it might be related to peace and quiet.
What does it mean to mind your P's and Q's?
english.stackexchange.com
<meaning>
english.stackexchange.com/questions/11997
english.stackexchange.com/users/618/John K
"Mind your Ps and Qs" means "be careful to behave well and avoid giving offence" and the earliest use of the expression appears to be in Thomas Dekker's play, "The Untrussing of the Humorous Poet" from 1602. However, some people believe that this phrase means "Mind your pints and quarts" or "mind your pleases and thank yous". Mind your "ps and qs" is understood to mean  behave well and do not give offence. The Noad traces it back to young students or children learning to spell, taking care to differentiate between "p" and "q" which are similar and so by extension it came to mean be careful of your language and be on your best behaviour. There is no date to when it was coined. Others understand it as relating to an innkeeper saying "mind your pints and quarts" to settle unruly customers.AUE also lists a few other theories,as  to its meaning: "Mind your 'please's and 'thank yous". There is also a suggestion that it comes from the printing business where the typesetting of the letter p and q  could easily be confused. Again a warning to take care and do things properly. A final theory is that it has to do with the two branches of the Celtic family of languages: P-celtic (i.e. Brythonic - Welsh etc.) and Q-celtic (i.e. Goideilic - Irish etc.) as the sounds were beginning to change, but is unlikely as the idiom seems mainly of English origin.
"Mind your Ps and Qs" means "be careful to behave well and avoid giving offence" and the earliest use of the expression appears to be in Thomas Dekker's play, "The Untrussing of the Humorous Poet" from 1602. However, some people believe that this phrase means "Mind your pints and quarts" or "mind your pleases and thank yous". This expression means to be on your best behaviour. The origin is unknown, but it could be a shortening of 'Pleases' (Ps) and 'Thank-yous' (Qs) or a reference to the ease of confusing the two letters when writing by hand or using a print type block.
To mind your P's and Q's means be on your best behaviour; be careful of your language and avoid giving offence. Possibly short for Mind your Pints and Quarts! No one is sure of the origin, but possibly it is thought it was to remind people in the printing business, to be careful when typesetting 'p' and 'q', because it was easy to confuse the two. Or possibly from when these were beginning to separate and you had to get the pronunciation right in each area to be understood. Another explanation, probably apocryphal - is that it has to do with the two branches of the Celtic family of languages: P-celtic (i.e. Brythonic - Welsh etc.) and Q-celtic (i.e. Goideilic - Irish etc.). The phrase "Mind your P's and Q's" is generally agreed to be a warning to behave well and avoid giving offence. However, it's origins are less clear. Some people believe it was a warning to typesetters not to confuse their numbers, whilst others believe it may have been a warning for people to take care over their pronunciation. There is also the claim that it originally meant "Mind your pints and quarts".
Mind your Ps and Qs" means "be careful to behave well and avoid giving offense. Originally short for "Mind your Pints and Quarts!"  Originated in the Printing business Originated when children were being trained to write to distinguish the letters. It coud be of celtic language source when the languages were dividing.
This expression means to be on your best behaviour. The origin is unknown, but it could be a shortening of 'Pleases' (Ps) and 'Thank-yous' (Qs) or a reference to the ease of confusing the two letters when writing by hand or using a print type block.
The phrase "Mind your P's and Q's" is generally considered to be a warning to behave well and avoid offending others. The phrase may have originated in the typesetting profession as a warning not to confused the letters p and q. The phrase may also have been a warning for people to take care over their pronunciation. The phrase may have originally been "Mind your pints and quarts".