ABSTRACT
Artificial intelligence.—Some theoretical results have indicated that it is impossible to reason by means of an expressive language if one wants to be both valid and efficient (→COMPLEXITY, LANGUAGE, REASONING AND RATIONALITY). The expressiveness of a given language L is not measurable; attempting to assess it in terms of how many things are expressible by a formula in L is unsatisfactory. Indeed, propositional logic supports a countable but infinite number of proposition symbols, and one is free to interpret each symbol by whatever statement one wants. But it cannot account for ordinary syllogisms (→LOGIC, SYMBOL).
