In accordance with the terms of the Barbour-Page Foundation, these lectures are published by the University of Virginia. The author owes his thanks to the authorities of the university for their courtesy in conforming to his wishes in respect to some important details of publication. With the exception of a few trifling changes the lectures are printed as delivered.

These lectures will be best understood by reference to some portions of Locke’s _Essay Concerning Human Understanding_. The author’s acknowledgments are due to _Locke’s Theory of Knowledge and Its Historical Relations_ by Professor James Gibson, to _Prolegomena to an Idealist Theory of Knowledge_ by Professor Norman Kemp Smith, and to _Scepticism and Animal Faith_ by George Santayana.

A. N. W.

Harvard University, June, 1927.