Trinity Coll., Dublin, June 21. 1851.
Replies to Minor Queries.
_Mind your P's and Q's_ (Vol. iii., pp. 328. 357. 463. 523.).--I have
always thought that the phrase "Mind your P's and Q's" was derived from
the school-room or the printing-office. The forms of the small "p" and
"q" in the Roman type, have always been puzzling to the child and the
printer's apprentice. In the one, the down-ward stroke is on the left of
the oval; in the other, on the right. Now, when the types are reversed,
as they are when in the process of distribution they are returned by the
compositor to his case, the mind of the young printer is puzzled to
distinguish the "p" from the "q." In sorting _pie_, or a mixed heap of
letters, where the "p" and the "q" are not in connexion with any other
letters forming a word, I think it would be almost impossible for an
inexperienced person to say which is which upon the instant. "Mind your
_p_'s and _q_'s"--I write it thus, and not "Mind your P's and Q's"--has
a higher philosophy than mind your _toupées_ and your _queues_, which
are things essentially different, and impossible to be mistaken. It
means, have regard to small differences; do not be deceived by apparent
resemblances; learn to discriminate between things essentially distinct,
but which look the same; be observant; be cautious.