Taxon names, not taxa, are defined

In commenting on the draft Phylogenetic Code of Biological Nomenclature or PhyloCode (Cantine & de Queiroz, 2000), Stuessy (2000) argued that, contrary to the wording in that document, taxon names are not defined. Although one of us presented a counter-argument including evidence that taxon names are indeed deñned (de Queiroz, 2CKX)), Stuessy (2001) has reiterated and elaborated on his earlier proposition, asserting as well that the PhyloCode is not purely a system of nomenclature but rather a combined taxonomic and nomenclatura! system and that it is two-ranked. Here we argue that Stuessy's proposition that taxon names are not defined is still incorrect and results from his both failing to recognize different kinds of definitions and confusing different meanings of the term "definition". We also argue, countering Stuessy's other assertions, that the PhyloCode separates nomenclature from taxonomy more successfully than do the codes of rank-based nomenclature, such as the International Code of Botanical Nomenclature (¡CBN; Greuter & al., 2000), and that the categories "clade" and "species" of the PhyloCode are not ranks. Stuessy begins his paper with a discussion of organisms (individuals) and their names. According to Stuessy, "Individuals can be described, or if you like defined (my preference would be 'characterized'), but not their names" (p. 185). On the contrary, individuals can be described or characterized but not defined; only their names can be defined (e.g., Ghiselin, 1966a, b, 1984). The reason is that "Definitions apply only to words, not to the things to which the words correspond" (Ghiselin, 1966a: 127). Stuessy states that names differ from other words in that they are "solely labels for purposes of communication" and that they are bestowed by "christening" (p. 185). These statements suggest that his objection has to do with the propositions that the names of individuals are proper names and that the proper names of individuals cannot be defined intensionally•that is, in terms of necessary and sufficient (defining) properties (e.g., Ghiselin, 1984; but see Kripke, 1980: 112115). These propositions do not, however, rule out the possibility of defining proper names. The reason is that names can be defined by other means than necessary and sufficient properties; in particular, they can be defined ostensively•that is, by pointing (e.g., Ghiselin, 1984). The act of pointing constitutes a definition in that it specifies the meaning or reference of a word.