Books to understand photography: David Hurn & Bill Jay - On Being a Photographer.
This book is the best and most useful guide of photography you'll ever find.
David Hurn is a great magnum photographers and photo collector. In conversation with Bill jay, they explore the practical nuances of photography.
David approaches the clear thinking of your work method; The importance of the subject; How to organize and prepare a photo project; The process of taking a single photograph; The appreciation of other photographers and so on.
This is a must read for those being serious about photography, beyond photo tips and tricks and how to expose well and camera gear discussions.