reiter@endor.harvard.edu (Ehud Reiter) (01/18/89)
Steve Harnad writes >"Information content" depends on resolving uncertainty. Objective >uncertainty is a function of objective consequences: It matters >whether this is a "mushroom" or a "toadstool," because if I miscategorize, >I may die. To the extent that categorization is guided by objective >consequences, it is nonarbitrary ... The problem here is who makes up the categories? Professional biologists don't particularly care if a plant is poisonous or not, or if an animal is edible - they're much more interested in organ structure, evolutionary history, biochemical details, and so forth. The categories they come up with are pretty good at predicting such details, but they're much less useful at predicting more mundane attributes like edibility. So, the categories used by professional biologists may not be very useful to the average language user. This would not matter, except for the fact that the language community at large has been trying to align its biological categories with the ones used by biologists. So, the community has decided that "bird" means a member of class Aves, and thus penguins are birds, but bats are not. Similarly, "fish" means member of class Agnatha, Placodermi, Chondrichthyes, or Osteichthyes. Thus, a whale is not a fish, since it is a member of class Mammalia. In short, how useful modern English biological categories are to the average language user (as opposed to the professional biologist) may be questionable. >[Categories] may or may not be human creations, but they must be based on >objectively observable features if they are to be reliably picked out >(as they are). Cladistic and evolutionary taxonomists define categories phylogenetically, not in terms of observable physiological features (see my previous posting). Identification procedures that are based on observable features can usually be constructed, although these may be based on "family resemblance" ideas. From Ernst Mayr, PRINCIPLES OF SYSTEMATIC ZOOLOGY, pg 88 "As a heritage from the days when classification was considered synonymous with identification, there is an erroneous concept of the higher taxon, or rather the members of a higher taxon, as the carriers of an identifying character. A taxon is in fact a group of [evolutionary] relatives, and whether or not they have the same "characters in common" is irrelevant. Many taxa are based on a combination of characters, and frequently not a single one of these characters is present in all members of the taxon, yet such a taxon may have a sound "polythetic" basis." ["polythetic" means "Each species possesses a large (but unspecified) number of the total number of properties of the taxon" - page 83] I question whether an average language user is in fact capable of always reliably identifying a "bird", a "mammal", or a "fish" (i.e. a member of class Aves, class Mammalia, or classes {Agnatha, Placodermi, Chondrichthyes, Osteichthyes}). We are taught some special cases in school (e.g. "penguins are birds, but bats are not", "whales aren't fish, they're mammals"), but I suspect we would fail on other unusual cases that are not taught in school (e.g. pterodactyls and ichthyosaurs). Hilary Putnam (e.g. in "The Meaning of 'Meaning'", chap 12 in MIND, LANGUAGE, AND REALITY) has suggested that definitions can make reference to expert knowledge (e.g. "I don't know whether an ichthyosaur is a fish or a reptile, but I know who to ask to find out"). This sounds like as good a suggestion as any for how the average language user defines biological categories. Ehud Reiter reiter@harvard (ARPA,BITNET,UUCP) reiter@harvard.harvard.EDU (new ARPA)