In The Poverty of the Linnaean Hierarchy, Marc Ereshefsky, a professor of philosophy at the University of Calgary, offers a survey of competing philosophies of classification, articulates and defends a form of pluralism with regard to species concepts, and argues that the Linnaean system ought to be abandoned in favor of a post-Linnaean, rank-free, phylogenetic taxonomy (like PhyloCode, with a few differences). Elliott Sober writes, "This book is of practical importance to biologists, but its analysis of the relationship between theories and classification schemes will also be of compelling interest to philosophers of science."