In Reply to: Mind your p's and q's posted by Gary Martin on November 30, 2008 at 17:57:
: : I recently met a student of the Irish language who told me of two distinct types of Gaelic (Gallic)dialects spoken in Ireland, which are colloqially referred to as "P" and "Q". When we think about language use as a social marker, it struck me that there would be a fair amount of importance attached to the choice of one's use of a dialect. Has anyone else considered that this might be the origin of the English phrase "Mind your p's and q's"?
: I've researched this phrase in the past and haven't come across that version of the proposed origin before. The fact that it is a little known suggestion counts against it being correct. If it were correct, surely we would have heard of it sooner.
Another fact that counts against it is that it is simply not true! The Celtic group of languages falls into two groups, traditionally known as "Q-Celtic" (which includes Scots and irish Gaelic) and "P-Celtic" (which includes Welsh, Cornish and Breton). They are so named because the main difference between them is that words which in one group have a "Q" or "K" sound have a "P" sound in the other group; e.g. the words for "head" and "four" in Gaelic are "ceann" and "ceithir", and in Welsh are "pen" and "pedwar".
But there has never been any P-Celtic language spoken in Ireland, and if your informant had been genuinely a "student of the Irish language", s/he would have known this. In any case, the phrase "mind your P's and Q's" is first attested in the 18th century, at which time the average English person's knowledge of Celtic tongues was nil, and even scholars had not yet analysed their relationships into the Q- and P- groups. So this suggestion is certainly nonsense. (VSD)