Posted by Edward Stansell on September 13, 2002
I agree with you that the most
plausible origin for mind your P's & Q's is from the job of compositor or typesetter.
The "printer's devil" (apprentice) was told this because of the similarity between
the lower case of these letters and the fact that they are located next to one
another in the type case. Anyone who has set type can testify that the saying
could almost as likely been watch your b,d,p,q,n and u. I suppose that was too
big a mouthful. Type is in the reverse of the printed letter but is relatively
easy to read if arranged in words, however, individual characters can be difficult;
particularly those I've mentioned.