Folks, (01) I have been making some strong criticisms about upper-level ontologies, even though I have been working on and writing about such things for many years. (02) I haven't completely given up on the idea that an upper level is useful, but over the years, I have come to the conclusion that any upper level should be as *neutral* as possible -- i.e., it should not be biased for or against anybody's pet theories, and it should not contain any axioms that contradict any of the specialized axioms that anybody might need in any application at any lower level. (03) These criteria imply that the upper levels should have very few axioms. Following are some kinds of axioms that should *not* be in the upper levels: (04) 1. Any axioms that make empirical claims that might be falsified by future experiments or any claims that are known to be false in detail, but which may be useful approximations for many purposes. For example, the upper levels should be neutral with respect to a Newtonian view vs. any more modern theory of physics because for many practical purposes a Newtonian description is accurate within the granularity of the usual measuring instruments. (05) 2. Any axioms that require, prefer, or rule out one kind of representation over another, such as a four dimensional vs. a (3+1) dimensional description of space and time. (06) 3. Any axioms that rule out exceptional cases that may be rare, but possible. For example, it should not say that a tiger has four legs, because some tigers might be born with more than four and some might lose a leg. In fact, there might be quadriplegic tigers that get around in some prosthetic device. (07) 4. Any axioms that imply a vase and the clay it consists of are or are not identical, because many respectable theories make different claims in that regard. They should also avoid all claims about whether a child is identical or not identical to the adult at some later stage of life -- because some theories say yes, others say no, and other treat the question as context-dependent (i.e., identical for inheritance issues, but not identical for employment). In fact, the entire issue of identity claims is so full of conflicting philosophical positions that the upper levels should *not* make any identity claims of any kind. (08) 5. Any axioms that imply physical objects and processes are disjoint. Some theories say they must be disjoint, others say they may overlap, and others say that object and process descriptions are complementary ways of describing the same phenomena. (09) 6. Any axioms about artifacts that may be falsified by developments in technology. For example, the attached phone.gif example is taken from a dictionary published in 1969, but very few of the features depicted are common in the telephones manufactured today. However, the definition in that dictionary is still true: "an instrument for reproducing sounds at a distance." (010) 7. Any axioms that distinguish essential properties from accidental properties. This issue has been debated since the time of Plato and Aristotle. The traditional definition of Human is Rational Animal, and the ability to laugh was considered an accidental property. However, many philosophers have claimed that the ability to laugh is just as characteristic of humans and more easily defined than the ability to reason. Today, genes are considered more fundamental to what is "essential", but that makes it harder to distinguish humans from chimps and bonobos. A truly neutral upper level should avoid any commitment to what is considered essential vs. what is considered accidental. (011) When you start to analyze the issue, the number of possible conflicts becomes so large, that the safest position with regard to any axiom in the upper levels is very short: When in doubt, leave it out. (012) That definition of telephone from 1969, which is still true today, suggests the kind of information that might be included in an upper level: a definition or axiom that is true because of the intended function of an artifact. Unfortunately, it is very difficult to state such definitions in full generality and even more difficult to find formally defined relations that can be used to state them. (013) For example, how can the words "instrument", "reproduce", "sound", and "distance" be defined in a precise, but general way? And how could they be defined in a way that would distinguish a telephone from a radio? And would you want to distinguish telephones from radios? If you did, that would rule out cell phones, which are in fact radios and can be used to reproduce radio programs and even television programs. In fact, cell phones are now being used as cameras and even TV cameras that broadcast live events over the Internet. (014) If you want the upper levels to be sufficiently general, you can't put many axioms into them. They become, in fact, just what I said in my previous notes: a cleaned-up version of WordNet. It's not an accident that WordNet is so widely used, because it performs a needed function. Anything that is more detailed than WordNet would be too constrained and too inflexible to be useful for relating one general-purpose ontology to another. (015) For deduction, however, inflexibility and constraints are necessary to support detailed proofs. But those constraints will inevitably create contradictions with very important developments in technology. If you define the word "telephone" in such a way that makes it disjoint with radios, TVs, and cameras, then you rule out cell phones -- or perhaps you may permit very simple cell phones, but you rule out any kind of new technology without making a major category shift. (016) Summary: When you examine all the conditions and applications that an upper-level ontology must serve, you discover that it is very hard to distinguish it from a cleaned up terminology. It is clear that we need detailed axioms in the microtheories, but it is not at all clear whether we need an upper level that is distinct from a terminology. (017) John Sowa (018)
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