 He is a member of the Highlands Institute of American Religious and Philosophical Thought (HAIRPT) and has been a leader in the discussions on Religious Naturalism.Crosby is a Religious Naturalist having contributed to the movement with six books and a number of journal articles and chapters in books.He argues that nature itself, without notions of God, gods, animating spirits, or supernatural beings or realms of any kind, is both metaphysically and religiously ultimate, and thus an appropriate and compelling focus of religious commitment and concern.