As Professor Ritchie's published works are concerned mainly with ethics and politics, it seemed to me that this posthumous volume should represent, as adequately as is now possible, the philosophical position that underlies his practical doctrine. I have therefore devoted the greater part of the Memoir to a connected exposition of his views in philosophy, and my aim has been, by full quotations from the notebooks, letters and other manuscripts which Mrs. Ritchie has kindly entrusted to me, to express his ideas as far as possible in his own words. As he wrote on these high subjects in a fresh and untechnical style, I hope that many readers, who know only his political and ethical writings, may find these studies illuminating and suggestive.