ABSTRACT
In an argument tending to cast doubt on the idea that there is a mental logic, Evans (1993) wrote, “Formal logic is an inaccurate and unnatural representation of reasoning involving natural language and real-world concepts” (p. 12). The editors and the other contributors to this volume agree with Evans on this point. Standard logic is indeed unnatural in many ways that make it unfit as a model of any part of ordinary human reasoning. For instance, to ordinary intuition, an if-then sentence is not true merely because its if-clause is false, as it is in standard logic; it is also highly counterintuitive, to take another example, that, merely because there are no unicorns, both the propositions “Every unicorn has a horn” and “No unicorn has a horn”1 should come out true. Furthermore, the frequent gross lack of correspondence between the syntactic structures of propositions in standard logic and those of the sentences of English or any other language with the same meaning (I provide some examples later) also creates a serious problem for the idea that people reason with standard logic: Why should the natural language (in which we often think we are reasoning) be so different in structure from standard logic, if we are indeed reasoning in standard logic? The natural language syntactic structure is unmotivated.
