Commonplace books are a little like personalized encyclopedias: places to write down tidbits of knowledge gleaned from the world, like aphorisms, lines of verse, lyrics or memorable movie quotes; they might also include recipes, prayers, portraits, mathematical formulas, maps or anything else useful and easily forgotten. Unlike journals or diaries, these notes are not usually the owner’s original thoughts, and thus offer a different kind of window into their mind. In these pages are things perhaps even more intimate than secrets: desires, passions, aspirations.

Arguably, the commonplace book dates back almost 2,000 years. In the second century, Marcus Aurelius’ Meditations began as his collection of ideas and quotations. Much later, in 14th-century Italy, zibaldone, or “hodgepodge...