enantiomers as testcase for the monism/pluralism debate in chemistry (..) minimal monist stance: monists might circumscribe their claim about kinds to the domains of, say, chemistry and physics (..) Let us say that a theory is ‘pluralist’ with respect to natural kinds if it admits of more than one way of carving up the world. (..) Quine finds objectivism about chemical kinds lurking in chemical structure. If such properties are objective, then we have an objective notion of comparative similarity and hence a good candidate for monistic chemical kindness. (..) Putnam and Kripke, free from Quine’s antiessentialist scruples, suggest that the 'real essence' of a kind (what it is to be a kind of thing) is having a certain structure. (..) Recognizing any structural (or perhaps even any intrinsic) difference as demarcating a difference in kind seems to entail a problematic instability in our classifications. (e.g. (generally) stable nuclear properties) (..) Putnam suggests that it is the essence of water to have the chemical structure represented by ‘H2O’ and that this was a discovery. (..) D20 (heavy water) other properties (e.g. fuel for hydrogen-bomb (..) if the extensions of kinds are artifacts of human classificatory conventions, then they are not at bottom objective, let alone monistic. (..) Dupre´ mentions two desiderata for a robust kinds ontology (1993, 17): 1. Distinctions should be sharp (in at least a serviceable way). 2. Classifications should be discovered rather than merely invented. (..) What properties and dispositions we wish to regard as demarcating important lines of classification depends on our standpoint. (..) Monism is a thesis about the actual kind distinctions (what natural kinds there are), not about the various ways we ignore those distinctions in cobbling together a workable system of classification. Classificatory pluralism does not entail metaphysical pluralism. (..) the real essences of natural kinds are intrinsic properties, not relational properties. (Wilkerson 1995, 32) (..) Enantiomorphs, ever a source of philosophical puzzlement, provide an interesting test case for such a theory of chemical kinds. Prima facie, enantiomorphs have different dispositions, but similar structures. How, then, should we regard them? May enantiomorphs be of distinct natural kinds? For any progress to be made, it seems, at least two other questions must be answered: Do enantiomorphs differ in internal structure? and Do enantiomorphs differ dispositionally? (..) e.g. left hand - right hand (..) The phenomenon of chirality was instrumental in the development of stereochemistry. (..) Pasteur observed that solutions made from lefty crystals rotated light in the opposite direction from those made from righty crystals, deducing that optical activity had to do with the spatial arrangement of atoms. Molecules could be 'handed'. Such differently handed chemical species are referred to as ‘enantiomers’. (..) The question of whether enantiomorphs differ structurally is notoriously controversial. Perhaps we ought to distinguish the concept of structure from that of internal structure, where the latter is to be understood as excluding spatial embedding or handedness. (..) The monist simply incorporates chirality into the notion of molecular structure, regarding it as a primitive internal feature. (..) our amino acids are exclusively of the ‘L-’ configuration; the sugars we use exclusively of the ‘D-’ configuration. Hence the biological effects of enantiomers may differ widely despite their sharing a great many other properties (..) abandon internal structure as a privileged dividing line and to regard their different biological dispositions as marking them off as distinct kinds. (..) According to the monist, there may be many different, appropriate, eminently justifiable schemes of classification that sit atop a robust ontology of chemical and physical kinds, perhaps characterized by real essences. If the world has a unique, essential structure, nothing says that even if we came to appreciate this structure, it would impel a unique taxonomy. Perhaps the world has far more unique structure than we are interested in countenancing. A most natural (and monistic-metaphysicsfriendly) pluralism concerns the various legitimate ways this structure can be ignored. (..) enantiomers as distinct natural kinds appears to me plausible. So, however, does the view on which their (apparent) difference outstrips the resources we might accord a theory of natural kinds: there is much we can say about the world without overt reference to natural kinds. (..) it ought to be open to the essentialist, in honoring her philosophical commitments, to regard enantiomers merely as a telling example of the limited value of a kinds ontology to science. Perhaps the most coherent understanding of these facts is that the world 'supports' either ontology - that is, that it is pluralistic (at least, to a degree). |