Book excerpt: "The Value of Philosophy" is one of the most important chapters of Bertrand's Russell's magnum Opus, The Problems of Philosophy. As a whole, Russell focuses on problems he believes will provoke positive and constructive discussion, Russell concentrates on knowledge rather than metaphysics: If it is uncertain that external objects exist, how can we then have knowledge of them but by probability. There is no reason to doubt the existence of external objects simply because of sense data.