Commonplace book

A commonplace book helps you process, understand, and retain anything that’s valuable to you^[1].

“a central resource or depository for ideas, quotes, anecdotes, observations and information you come across during your life and didactic pursuits.” In other words, a “thinker’s journal.”^[2]

Cognitive scientists say creative thinking can come from connecting disparate ideas that wouldn’t otherwise cross paths.^[1:1]

Peter Beal, leading expert on English manuscript studies, defines a commonplace book as

“a manuscript book in which quotations or passages from reading matter, precepts, proverbs and aphorisms, useful rhetorical figures or exemplary phrasing, words and ideas, or other notes and memoranda are entered for ready reference under general subject headings.”
~ A Dictionary of English Manuscript Terminology 1450-2000

A commonplace book is as much about making connections between various ideas as anything else in personal knowledge management. It's not just about collecting interesting quotes and passages. Though that can be useful too, it's easy to fall into the the collector's fallacy.

Let us take down one of those old notebooks which we have all, at one time or another, had a passion for beginning

See: zibaldone for the Italian renaissance style of commonplacing

See Zettelkasten for the index card based successor to the Commonplace book