Bertrand Russell

Is there any knowledge in the world which is so certain that no reasonable man could doubt it?

© Bertrand Russel, "Problems of Philosophy", Chapter I, Appearance and Reality.

A belief is true when it corresponds to a certain associated complex, and false when it does not.

© photo by Derek Shapton
© Bertrand Russel, "Problems of Philosophy", Chapter XII,Truth and Falsehood.

Philosophy is to be studied, not for the sake of any definite answers to its questions since no definite answers can, as a rule, be known to be true, but rather for the sake of the questions themselves; because these questions enlarge our conception of what is possible, enrich our intellectual imagination and diminish the dogmatic assurance which closes the mind against speculation; but above all because, through the greatness of the universe which philosophy contemplates, the mind also is rendered great, and becomes capable of that union with the universe which constitutes its highest good.

© Bertrand Russel, "Problems of Philosophy", Chapter XV, The Value of Philosophy.