 Wright's writings are contained in two volumes, Philosophical Discussions, a collection of his articles published in American and British periodicals of the time, and Letters, collected shortly after his death by his friend James B.  Thayer.[4]  Two fundamental epistemological themes are prominent throughout his work: 1) sense perception provides the only evidence whose authority all humankind acknowledges, and 2) sense experience alone can produce the conviction and permanence that we believe knowledge should have. The first point addresses the problem of the diversity of truth claims, the second the expectation that genuine truth claims not be superseded. He said: