 In Cambridge, Royce commenced to work doggedly and in diverse areas. In January 1883 he arrived at an insight that proved fundamental to his philosophy: in order for our ordinary concepts of truth and error to be meaningful, there must be an Absolute Knower, an actual infinite mind that encompasses the totality of all actual truths and possible errors. This insight formed the core of his first major philosophical publication, The Religious Aspect of Philosophy, which appeared in 1885. Royce received a permanent appointment as assistant professor at Harvard in that same year. (During his three decades at Harvard Royce would teach such notable students as T. S. Eliot, George Santayana, and W. E. B. Du Bois.) He taught full time, gave many public lectures, published his History of California in 1886, and a novel in 1887. In 1888 he experienced a nervous breakdown, from which he recovered after a sea voyage of some months’ duration.