From Thomas Jefferson and Charles Darwin, to Oscar Wilde and Ralph Waldo Emerson, great thinkers throughout history did more than read the books they picked up. Many wrote and stored the most useful, profound passages in something called a Commonplace Book—an easily review-able collection of wisdom and ideas for their personal use.

We humans forget much more than we remember. The Commonplace Book was a sort of outboard memory, a way to keep and revisit our most insightful insights. In the 18th and 19th centuries, these collections of wisdom were so popular that "commonplacing" was an actual term for the act of writing in your Commonplace Book.

Somewhere along the line, Commonplace Books retreated from popular culture, yet thankfully, never disappeared completely. A year and a half ago, I discovered and began to build my own based on the index card system of one of my favorite authors. Today, I'm 56 books in and have over one thousand index cards comprising my Commonplace Book. I recently filled up my first "shoe box" of index cards, a milestone that inspired me to finally write this article.