The Role of Logic and Ontology In Language and ReasoningJohn F. SowaAbstract. Natural languages have words for all the operators of first-order logic, modal logic, and many logics that have yet to be invented. They also have words and phrases for everything that anyone has ever discovered, assumed, or imagined. Aristotle invented formal logic as a tool (organon) for analyzing and reasoning about the ontologies implicit in language. Yet some linguists and logicians took a major leap beyond Aristotle: they claimed that there exists a special kind of logic at the foundation of all NLs, and the discovery of that logic would be the key to harnessing their power and implementing them in computer systems. Projects in artificial intelligence developed large systems based on complex versions of logic, yet those systems are fragile and limited in comparison to the robust and immensely expressive natural languages. Formal logics are too inflexible to be the foundation for language; instead, logic and ontology are abstractions from language. This reversal turns many theories about language upside down, and it has profound implications for the design of automated systems for reasoning and language understanding. This article analyzes these issues in terms of Peirce’s semiotics and Wittgenstein’s language games. The resulting analysis leads to a more dynamic, flexible, and extensible basis for ontology and its use in formal and informal reasoning. This article is a slightly revised preprint of Chapter 11 in Theory and Applications of Ontology: Philosophical Perspectives, edited by R. Poli & J. Seibt, Berlin: Springer, pp. 231-263. 1. The Search for FoundationsNatural languages are the most sophisticated systems of communication ever developed. Formal ontologies are valuable for applications in science, engineering, and business, but they have been difficult to generalize beyond narrowly defined microtheories for specialized domains. For language understanding, formal systems have only been successful in narrow domains, such as weather reports and airline reservations. Frege, Russell, and the Vienna Circle tried to make formal logic the universal language of science, but that attempt failed. Only the final results of any research can be stated formally, never the vague hunches, intuitive explorations, and heated debates that are necessary for any creative advance. Scientists and engineers criticized formal methods with the pithy slogans “Physicists don’t do axioms” and “All models are wrong, but some are useful.” Even Aristotle, who invented the first formal logic, admitted that his syllogisms and categories are important for stating the results of research, but that informal methods are necessary for gathering and interpreting empirical evidence. Aristotle’s logic and categories still serve as a paradigm for the ontologies used in modern computer systems, but his grand synthesis began to break down in the 16th century. Aristotle’s physics and cosmology were demolished by the work of Copernicus, Galileo, Kepler, and Newton. In philosophy, the skeptical tradition of antiquity was revived by the publication in 1562 of a new edition of the works of Sextus Empiricus, whose attacks on Aristotle were popularized by the essays of Michel de Montaigne. In responding to the skeptics, Descartes began his search for certainty from the standpoint of universal doubt, but he merely reinforced the corrosive effects of skepticism. The British empiricists responded with new approaches to epistemology, which culminated in Hume’s devastating criticisms of the foundations of science itself. Two responses to Hume helped to restore the legitimacy of science: Thomas Reid’s critical common sense and Immanuel Kant’s three major Critiques. Kant (1787)
