"A book, like a landscape, is a state of consciousness varying with readers. There exists some book, pamphlet, article in an encyclopaedia, or possibly an old clipping from a newspaper that once set you thinking; there may be many; indeed you may be one of those rare beings with whom a few lines of print are food enough or thought because, as Lamartine says, their thoughts think themselves. The sometimes evocative for you may be poetry, history, philosophy, the sciences, or moral sciences, i.e. the progress of mankind. Some people who go to sleep over a volume will be interested by a review which they think more condensed or better within their reach. Read reviews if they help you to think, that is. to say if they leave in your mind images that will go on living when you have forgotten where they came from. Read a Shakespeare calendar at the rate of four lines a day, if Shakespeare quotations have on you the magic influence they have on some people; read algebra, read the lives of great inventors or of great businessmen, read that kind of books which you and nobody else know to be thought-productive for you."