Occam’s Razor in science: a case study from biogeography

There is a widespread philosophical presumption – deep-rooted and often unarticulated – that a theory whose ontology exceeds that of its competitors is at a prima facie disadvantage. This presumption that ontologically more parsimonious theories are preferable appears in many guises. Often it remains implicit. Sometimes it is invoked as a primitive, self-evident proposition that cannot be further justified or elaborated upon (for example at the beginning of Goodman and Quine’s 1947 paper, and in Quine’s remarks about his taste for ‘‘clear skies’’ and ‘‘desert landscapes’’). Other times it is elevated to the status of a ‘‘Principle’’ and labeled as such (for example, the ‘‘Principle of Parsimony’’). However, perhaps it is best knownby the name ‘‘Occam’s (orOckham’s)Razor.’’ The question I wish to address in this paper is whether Occam’s Razor is a methodological principle of science. In addition to being a significant issue in its own right, I am also interested in potential connections between attitudes towards parsimony in science and in philosophy. Metaphysicians might once have aimed to justify the use of Occam’s Razor in science by appeal to a priori philosophical principles. The rise of scientific naturalism in the second half of the 20th Century has undercut this style of approach. If anything, the direction of potential justification is reversed. Philosophy of science is conceived of as continuous with science, and not as having some independently privileged status. The perspective of the naturalistic philosopher may be broader, but her concerns and methods are not fundamentally different from those of the scientist. Thus scientific methodology neither needs, nor can legitimately be given, external philosophical justification. It is against this broadly naturalistic background that I am raising the above question: is Occam’s Razor a principle of science? My main case study, presented in Part 2 of the paper, is taken from biogeography. This is a field which has been studied in detail by historians of