Wikipedia:  Mind your Ps and Qs is an English language expression meaning "mind your manners", "mind your language", "be on your best behaviour", "watch what you're doing" or similar.

In the late 19th century, when literacy was relatively common in European countries such as the United Kingdom, the "Man of Letters" (littérateur)[17] denotation broadened to mean "specialized", a man who earned his living writing intellectually (not creatively) about literature: the essayist, the journalist, the critic, et al. In the 20th century, such an approach was gradually superseded by the academic method, and the term "Man of Letters" became disused, replaced by the generic term "intellectual", describing the intellectual person. In late 19th century, the term intellectual became common usage to denote the defenders of the falsely accused artillery officer Alfred Dreyfus.[18]