On concept formation in systematics

In his Grundzuge einer Theorie der phylogenetischen Systematik, Hennig (1950) cited three philosophers: the leading empiricist Rudolf Carnap, the conventionalist Hugo Dingler, and the somewhat more obscure empiricist Theodor Ziehen. David Hull characterized Hennig's Grundzuge as one long argument against idealistic morphology. It will here be argued that Hennig attacked idealistic morphology (synonymous with systematic morphology) for its mode of concept formation. Building on Carnap and Ziehen, who both looked back on Ernst Cassirer, Hennig argued that the generic, thing or class concept of traditional nomothetic science must be replaced with Cassirer's relation concept. According to Hennig, such emancipation of systematics from the Aristotelian species concept would also allow transcendence from the distinction of idiographic from nomothetic sciences, thus preserving the unity of science. However, the establishment of relations in the construction of a system of order presupposes entities that can be, or are, related. Relations presuppose relata, which in modern systematics are best conceptualized (at least at the supraspecific level) not as Aristotelian classes, nor as individuals as was argued by Hennig and Ziehen, but as tokens of natural kinds. (c) The Willi Hennig Society 2006.