Please quote or cite page numbers from published version only. Saul Kripke pointed out that whether or not an utterance gives rise to a liar-like paradox cannot always be determined by checking just its form or content. 1 Whether or not Jones’s utterance of ‘Everything Nixon said is true ’ is paradoxical depends in part on what Nixon said. Something similar may be said about the sorites paradox. For example, whether or not the predicate ‘are

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A very large body of work in AI begins with the assumptions that information and knowledge should be represented in first-order logic and that reasoning is theorem-proving. On the face of it, this seems implausible as a model for people. It certainly doesn’t seem as if we are using logic when we are thinking, and if we are, why are so many of our thoughts and actions so illogical? In fact, there are psychological experiments that purport to show that people do not use logic in thinking about a problem (e.g., Wason and Johnson-Laird 1972). I believe that the claim that logic is the language of thought comes to less than one might think, however, and that thus it is more controversial than it ought to be. It is the claim that a broad range of cognitive processes are amenable to a high-level description in which six key features are present. The first three of these features characterize propositional logic and the next two first-order logic. The last carries us beyond standard logic. I will express these features in terms of “concepts”, but one can just as easily substitute

Abstractions and metaphors seem necessary for human and software agents to operate on the Internet. We hear about (virtual) desktops, classrooms, universities, sales rooms, shopping baskets, etc. We investigate this from a logical point of view emphasizing the syntax/semantics distinction and the use of abstractions to handle logical and computational complexity.

Objects In this section, we discuss the following kinds of logical object: natural cardinals, extensions, directions, shapes, and truth values. The material concerning the latter four kinds of logical objects are presented here as new results of OT. However, before introducing those results, we first briefly rehearse the development of number theory in Zalta [1999].

Abstract: Can an epistemic conception of truth and an endorsement of the excluded middle (together with other principles of classical logic abandoned by the intuitionists) cohabit in a plausible philosophical view? In PART I I describe the general problem concerning the relation between the epistemic conception of truth and the principle of excluded middle. In PART II I give a historical overview of different attitudes regarding the problem. In PART III I sketch a possible holistic solution. Part I The Problem §1. The epistemic conception of truth. The epistemic conception of truth can be formulated in many ways. But the basic idea is that truth is explained in terms of epistemic notions, like experience, argument, proof, knowledge, etc. One way of formulating this idea is by saying that truth and knowability coincide, i.e. for every statement S

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