Q. What does 'mind your Ps and Qs' mean
A. It means 'to be careful'.
Q. How so
A. There's no definitive answer to that, as a number of theories have been put forward as to how the phrase came about.
Q. Such as
A. Well, one suggestion is that it started as a reminder to young children in the process of learning to write to make sure that they got their p and q the right way round - though the same could be said for b and d, and that has never been used. Another, related to this, is that the phrase originated in printing works, where apprentices would be urged to be careful when sorting type: given that type is reversed on a printing plate, it would be easy to mix the two letters up.
Q. Anything else
A. There are a couple of slightly more fanciful suggestions. First, that publicans running slates for their customers would use the code P for 'pint' and Q for 'quart' on the tab, thus it was important for them to make sure they 'minded' their Ps and Qs when totting up the bill. Second, French dancing masters at the time of Louis XIV, when huge wigs were all the rage, would warn their pupils to mind their Ps (pieds, 'feet') and Qs (queues, 'wigs'), in case they dropped their wigs while bowing.
Q. Are there any other phrases or sayings that use single letters in a similar way
A. Quite a few. Perhaps the first to spring to mind would be 'dotting the Is and crossing the Ts', meaning 'to be meticulous' or 'to pay close attention to detail'.
Other examples are: A-1, meaning 'first class' in Lloyd's Register of Shipping, and so, by extension, 'excellent'; A-team; A (or B or C) list; the alpha and omega, a euphemism for God, meaning 'the beginning and the end'; idiot 'with a capital I'; the three Rs (reading, 'riting and 'rithmetic, ho! ho!), though a more recent version, used by Jack Straw in 1999 in relation to a policy for dealing with young offenders, ran restoration (to the victim), reintegration (of the offender into the community) and responsibility (to be taken by offenders and their parents); U and Non-U, meaning 'upper-class' and 'non-upper-class'.
Q. What about Roman numerals (a bit of a mental leap there, admittedly)
I, II, III, IV (or IIII), V, VI, etc.
S = 7 (medieval Latin only, otherwise VII)
X = 10
XIX = 19
L = 50
R = 80 (but also LXXX)
LXXXIX = 89
N = 90 or 900 (what's 810 between friends )
C = 100
B = 300
D = 500 (in medieval Latin Q was used instead)
M = 1,000
MDCCCXC = 1,890
No wonder we use Arabic numerals.
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By Simon Smith