A logical expression of reasoning

A non-monotonic logic, the Logic of Plausible Reasoning (LPR), capable of coping with the demands of what we call complex reasoning, is introduced. It is argued that creative complex reasoning is the way of reasoning required in many instances of scientific thought, professional practice and common life decision taking. For managing the simultaneous consideration of multiple scenarios inherent in these activities, two new modalities, weak and strong plausibility, are introduced as part of the Logic of Plausible Deduction (LPD), a deductive logic specially designed to serve as the monotonic support for LPR. Axiomatics and semantics for LPD, together with a completeness proof, are provided. Once LPD has been given, LPR may be defined via a concept of extension over LPD. Although the construction of LPR extensions is first presented in standard style, for the sake of comparison with existing non-monotonic formalisms, alternative more elegant and intuitive ways for constructing non-monotonic LPR extensions are also given and proofs of their equivalence are presented.     

The truths of logic

Several accounts of logical truth are compared and shown to define distinct concepts. Nevertheless, conditions are given under which they happen to declare exactly the same sentences logically true. These conditions involve the variety of objects in the domain, the richness of the language, and the logical resources available. It is argued that the class of sentences declared logically true by each of the accounts depends on particularities of the actual world.     

Higher-order truths about chmess

Abstract Many projects in contemporary philosophy are artifactual puzzles of no abiding significance, but it is treacherously easy for graduate students to be lured into devoting their careers to them, so advice is proffered on how to avoid this trap.     

A logical calculus with descriptions

Journal of Philosophical Logic -     

A plea for logical objects

An account of validity that makes what is invalid conditional on how many individuals there are is what I call a conditional account of validity. Here I defend conditional accounts against a criticism derived from Etchemendy’s well-known criticism of the model-theoretic analysis of validity. The criticism is essentially that knowledge of the size of the universe is non-logical and so by making knowledge of the extension of validity depend on knowledge of how many individuals there are, conditional accounts fail to reflect that the former knowledge is basic, i.e., independent of knowledge derived from other sciences. Appealing to Russell’s pre-Principia logic, I defend conditional accounts against this criticism by sketching a rationale for thinking that there are infinitely many logical objects.     

A geometric interpretation of logical formulae

Summary The aim of this paper is to give a geometric interpretation of quantifiers in the intutionistic predicate calculus. We obtain it treating formulae withn free variables as functions withn arguments which run over an abstract set whereas the values of functions are open subsets of a suitable topological space.     

A dialogical route to logical pluralism

This paper argues that adopting a particular dialogical account of logical consequence quite directly gives rise to an interesting form of logical pluralism, the form of pluralism in question arising out of the requirement that deductive proofs be explanatory.

     

Memory for truths and falsehoods

Three experiments were carried out to determine whether recognition memory was more efficient for true statements (on the basis of the subjects’ stable body of knowledge) than for false statements. The first two experiments did not show any difference. In a third experiment, the distractors were structured to prevent subjects from responding on the basis of the familiarity of individual component words rather than on the basis of the complete sentences. This experiment showed a clear difference between sentence classes, with true sentences remembered more accurately and faster than false sentences. The data fit, in general, the hypothesis that true sentences are doubly represented in memory. The relation of these findings to the findings on the effects of encoding tasks is also noted.     

A logical calculus for controlled monotonicity

In this paper we introduce a new deductive framework for analyzing processes displaying a kind of controlled monotonicity. In particular, we prove the cut-elimination theorem for a calculus involving series-parallel structures over partial orders which is built up from multi-level sequents, an interesting variant of Gentzen-style sequents. More broadly, our purpose is to provide a general, syntactical tool for grasping the combinatorics of non-monotonic processes.     

A possible extension of logical theory?

Philosophical Studies -     

Negative truths and truthmaker principles

This paper argues that a consideration of the problem of providing truthmakers for negative truths undermines truthmaker theory. Truthmaker theorists are presented with an uncomfortable dilemma. Either they must take up the challenge of providing truthmakers for negative truths, or else they must explain why negative truths are exceptions to the principle that every truth must have a truthmaker. The first horn is unattractive since the prospects of providing truthmakers for negative truths do not look good neither absences, nor totality states of affairs, nor Graham Priest and J.C. Beall’s ‘polarities’ (Beall, 2000; Priest, 2000) are up to the job. The second horn, meanwhile, is problematic because restricting the truthmaker principle to atomic truths, or weakening it to the thesis that truth supervenes on being, undercuts truthmaker theory’s original motivation. The paper ends by arguing that truthmaker theory is, in any case, an under-motivated doctrine because the groundedness of truth can be explained without appeal to the truthmaker principle. This leaves us free to give the ommonsensical and deflationary explanation of negative truths that common-sense suggests.