Commonplace books (or commonplaces) are essentially handwritten scrapbooks filled with items of every kind: recipes, quotes, letters, poems, tables of weights and measures, proverbs, prayers, legal formulas, etc.
These commonplaces were used by readers, writers, students, and scholars as an aid for remembering useful concepts, or facts they had learned and each book would be unique to its owners particular interests. They became significant in early modern Europe.
Per Wiki, commonplace books are not diaries nor travelogues, with which they can be contrasted: English Enlightenment philosopher John Locke wrote the 1706 book A New Method of Making a Common Place Book, “in which techniques for entering proverbs, quotations, ideas, speeches were formulated. Locke gave specific advice on how to arrange material by subject and category, using such key topics as love, politics, or religion. Commonplace books, it must be stressed, are not journals, which are chronological and introspective.” – Nicholas A. Basbanes in “Every Book Its Reader: The Power of the Printed Word to Stir the World”
And in the words of Jonathan Swift: “A common-place book is what a provident poet cannot subsist without, for this proverbial reason, that “great wits have short memories;” and whereas, on the other hand, poets being liars by profession, ought to have good memories. To reconcile these, a book of this sort is in the nature of a supplemental memory; or a record of what occurs remarkable in every day’s reading or conversation. There you enter not only your own original thoughts, (which, a hundred to one, are few and insignificant) but such of other men as you think fit to make your own by entering them there. For take this for a rule, when an author is in your books, you have the same demand upon him for his wit, as a merchant has for your money, when you are in his.” —from “A Letter of Advice to a Young Poet”
Would you like to read more about commonplace books? Try these links:
How And Why To Keep A “Commonplace Book” at ThoughtCatalog
Commonplace Books at Harvard University Library