 Following upon his doctoral studies, he became an assistant professor of philosophy and religion at Centre College in Danville, Kentucky.In the fall of 1965 he began teaching religious studies and philosophy in the philosophy department at Colorado State University, from which he retired as Emeritus Professor of Philosophy in 2001.Crosby demitted the Presbyterian ministry in 1969 and began to develop his version of religious naturalism in writings dating from the early 1990s, reaching fuller expression in "A Religion of Nature" in 2002, and continuing to the present.