He introduces philosophy as a repeating series of (failed) attempts to answer the same questions: Can we prove that there is an external world?

Focusing 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.

[2] Russell guides the reader through his famous 1910 distinction between knowledge by acquaintance and knowledge by description[3] and introduces important theories of Plato, Aristotle, René Descartes, David Hume, John Locke, Immanuel Kant, Georg Wilhelm Friedrich Hegel and others to lay the foundation for philosophical inquiry by general readers and scholars alike.

In the following pages I have confined myself in the main to those problems of philosophy in regard to which I thought it possible to say something positive and constructive, since merely negative criticism seemed out of place.