Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!uwvax!rutgers.rutgers.edu!sri-spam!ames!sdcsvax!ucbvax!R20.UTEXAS.EDU!AI.CAUSEY From: AI.CAUSEY@R20.UTEXAS.EDU (Robert L. Causey) Newsgroups: comp.ai.digest Subject: Natural Kinds Message-ID: <12319416814.40.AI.CAUSEY@R20.UTEXAS.EDU> Date: Sat, 18-Jul-87 16:17:43 EDT Article-I.D.: R20.12319416814.40.AI.CAUSEY Posted: Sat Jul 18 16:17:43 1987 Date-Received: Tue, 21-Jul-87 00:42:51 EDT Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 114 Approved: ailist@stripe.sri.com In a message posted 7/15, John McCarthy says that philosophers have recently introduced the concept of natural kind, and he suggests how this concept may be useful in AI. I think this deserves serious comment, both historical and substantive. The following is lengthy, but it may illustrate some general characteristics about the relationships between philosophy and AI. HISTORY In their messages, Ken Laws and others are correct -- the idea of natural kinds is not new. It is at least implicit in some Pre-Socratic Greek philosophy, and Aristotle extensively developed the idea and applied it in both philosophy and biology. Aristotle's conception is too "essentialist" to fit what McCarthy refers to. In the late 1600's John Locke developed an impressive empiricist analysis of natural kinds. Further developments were contributed in the 1800's in J. S. Mill's, _A_System_Of_Logic_. Mill also made important contributions to our understanding of inductive reasoning and scientific explanation; these are related to natural kinds. In our century a number of concepts of natural kinds have been proposed, ranging from strongly empiricist "cluster" approaches (which need NOT preclude expanding the cluster of attributes through the discovery of new knowledge, cf. McCarthy 7/17), to various modal analyses, to some intermediate approaches. Any of these analyses may have some value depending on the intended application, but the traditional notion of natural kinds has almost always been connected somehow with the idea of natural laws. SUBSTANTIVE ISSUES 1. Whatever one's favorite analysis might be, it is important to distinguish between a NATURAL kind (e.g., the compound silicon dioxide, with nomologically determined physical and chemical attributes), and a functional concept like "chair". There is generally not a simple one-to-one correspondence between our functional classifications of objects and the classification systems that are developed in the natural sciences. This is true in spite of the fact that we can learn to recognize sand, penguins, and chairs. But things are not always so simple - Suppose that Rip van Winkle learns in 1940 to recognize at sight a 1940-style adding machine; he then sleeps for 47 years. Upon waking in 1987 he probably would not recognize at sight what a thin, wallet calculator is. Functional classifications are useful, but we should not assume that they are generated and processed in the same ways as natural classifications. In particular, since functional classifications often involve an abstract understanding of complex behavioral dispositions, they are particularly hard to learn once one gets beyond simple things like chairs and tables. 2. Even discovering the classic examples of NATURAL kinds (like the classification of the chemical elements) can be a long and difficult process. It requires numerous inductive generalizations to confirm that the attributes in a certain Set of attributes each apply to gold, and that the attributes in some other Set of attributes apply to iodine, etc. We further recognize that our KNOWLEDGE of what are the elements of these Sets of attributes grows with the general growth of our scientific knowledge. Also, we need not always use the same set of attributes for IDENTIFICATION of instances of a natural kind. Most of this goes back to Locke, and philosophers have long recognized the connection between induction and classification; Carnap, Hempel, Goodman, and others, have sharpened some of the issues during the last 50 years. 3. Now, getting back to McCarthy's suggestion -- in his second message (7/17) he writes: "...for a child to presume a natural kind on hearing a word or seeing an object is advantageous, and it will also be advantageous to built (sic) AI systems with this presumption." His 7/15 message says, "When an object is named, the system should generate a gensym, e.g., GOO137. To this symbol should be attached the name and what the system is to remember about the instance." This is an interesting suggestion, but it prompts some comments and questions: i) Assuming that children do begin to presume natural kinds at some stage of development, what inductive processes are they using, what biologically determined constraints are affecting these processes, and what prior acquired knowledge is directing their inductions. These are interesting psychological questions. But, depending on our applications, we may not even want to build robots that emulate young children. We can attach a name to a gensym, but it is not at all easy to decide "...what the system is to remember about the instance," or to specify how it is to process all of the stuff it generates in this manner. ii) Children receive much corrective feedback from other people; how much feedback will we be willing or able to give to the "maturing" robots? Will the more mature robots help train the naive ones? iii) Given that classification does involve complex inductive reasoning, we need to learn a lot more about how to implement effective inductive procedures, where "induction" is understood very broadly. iv) If the AI systems (robots, etc.) are to learn, and reason with, functional concepts, then things get even more complex. Ability to make abstractions and perform complex analogical reasoning will be required. In my judgment, we (humans) still have a lot to learn just about the representation of functional knowledge. If my Rip van Winkle story seems farfetched, here is a true story. I know a person who is familiar with the appearance and use of 5 1/4 inch floppy diskettes. Upon first seeing a 3.5 inch mini-diskette, she had no idea what it was until its function was described. Knowledge of diskettes can extend to tracks, sectors, etc. The concept of natural kinds is relatively simple (though often difficult to apply); functional concepts and their relations with physical structures are harder subjects. -------