His knowledge of books had in some degree diminished his knowledge of the world.

Shenstone suggests that reading can, paradoxically, narrow one’s grasp of reality if it becomes a substitute for lived experience. “Knowledge of books” implies secondhand understanding—systems, stories, and opinions mediated by authors—while “knowledge of the world” points to practical wisdom: how people behave, how institutions work, and how circumstances resist tidy theories. The phrase “in some degree” keeps the claim measured: books are valuable, but an excess of them may foster abstraction, pedantry, or naïveté about human motives. The aphorism thus advocates balance—learning tempered by observation, conversation, and experience.