I have to make grateful acknowledgment of the help which has been ungrudgingly rendered by my friend and colleague, Mr. Henry Barker, Lecturer in Moral Philo sophy in this University, who has carefully read the entire work both in manuscript and in proof, and whose advice has been of great value at many points. I have also to thank Mr. John Handyside, Lecturer in Philo sophy in the University of Liverpool, Mr. John Laird, Assistant in Moral Philosophy in the University of St. Andrews, and Mr. John Baillie, Assistant in Logic and Metaphysics in this University, for their kindness in revising the proofs, and for a number of important suggestions.