identifiable one would be named and studied within a phylogenetic context. What are currently called "species" represent different sorts of things depending on the sort of organisms and processes being considered. This is already the case, but is not formally recognized by those scientists using the species rank in their work. Adopting a rankless taxonomy at all levels would enhance academic studies of evolution and ecology and yield practical benefits in areas of public concern such as conservation.

of scientific revolutions. The philosophical foundations of systematic research are briefly reviewed as well as the structure and content of taxonomic theories. Most important research programs in systematics are outlined. The book includes analysis of the principal problematic issues as "scientific puzzles" in systematics.