In the present paper I argue that the two systems of phylogenetic nomenclature hitherto proposed represent, in a generalized sense, two different philosophies for how science develops and progresses. The phylogenetic system of definition. initially proposed by de Queiroz and Gauthier [Syst. Zool. 39 (1990) 307], and later labeled PSD, is typically Popperian in the 'sense that science progresses toward truth by An accumulation of knowledge. Phylogenetic definitions of taxon names are assumed to adapt automatically to each new hypothesis of phylogeny, thereby reflecting better and better hypotheses. The phylogenetic system of reference proposed by Harlin [Zool. Scr. 27 (1998a) 381], on the other hand, is more Kuhnian, because it is built on the idea that successive hypotheses are incommensurable (and thus not cumulative) and that taxon names might be equalled with low-level paradigms.