Several intrinsic/extrinsic distinctions amongst properties, current in the literature, are discussed and contrasted. The proponents of such distinctions tend to present them as competing, but it is suggested here that at least three of the relevant distinctions (including here that between non-relational and relational properties) arise out of separate perfectly legitimate intuitive considerations: though of course different proposed explications of the informal distinctions involved in any one case may well conflict. Special attention is paid to the question of whether a (...) single notion of property is capable of supporting the various distinctions. (shrink)

We consider the modal logic of non-contingency in a general setting, without making special assumptions about the accessibility relation. The basic logic in this setting is axiomatized, and some of its extensions are discussed, with special attention to the expressive weakness of the language whose sole modal primitive is non-contingency , by comparison with the usual language based on necessity.

For the claim that the satisfaction of certain conditions is sufficient for the application of some concept to serve as part of the (`reductive') analysis of that concept, we require the conditions to be specified without employing that very concept. An account of the application conditions of a concept not meeting this requirement, we call analytically circular. For such a claim to be usable in determining the extension of the concept, however, such circularity may not matter, since if the concept (...) figures in a certain kind of intensional context in the specification of the conditions, the satisfaction of those conditions may not itself depend on the extension of the concept. We put this by saying that although analytically circular, the account may yet not be inferentially circular. (shrink)

This paper considers the question: what becomes of the notion of a logic as a way of codifying valid arguments when the customary assumption is dropped that the premisses and conclusions of these arguments are statements from some single language? An elegant treatment of the notion of a logic, when this assumption is in force, is that provided by Dana Scott's theory of consequence relations; this treatment is appropriately generalized in the present paper to the case where we do not (...) make this assumption of linguistic homogeneity. Several applications of the resulting concept of a heterogeneous logic are suggested, but the main emphasis is on the formal development. One topic touched on is a certain contrast between the boolean and the intensional sentence-connectives in this more general setting. (shrink)

An account of desire as a species of belief may owe its appeal to the details of its proposal as to precisely what sort of beliefs desires are to be identified with, and its downfall may be due to those details it does provide. For example, it may be proposed that the desire that α is in fact the belief that it ought to be that α, or is morally good or desirable that it should be the case that α. (...) Here the appeal might be that of forging a link between the holding of a moral belief and the acknowledgment that one has a reason for acting a certain way; and the shortcoming of the suggestion is its evident implausibility: even if the ‘necessity’ direction could be established, having a desire hardly seems sufficient for the holding of any such belief. Again: it might be proposed, perhaps simply to bring some order into the realm of propositional attitudes by reducing some to others, that the belief with which we should identify a’s desire that α is a’s belief that he will or would be happy if α. This proposed identification can be seen to be incorrect by consideration of examples such as the following, due to J. Gosling. An aging and ailing parent might forego numerous pleasures in order that his children should reap the benefits of his saving and have a good start in life – perhaps by receiving an expensive education – after his impending death. Oearly he may want that they should so benefit even if he does not believe in an after-death existence in which he might come to know of, and so take pleasure in, his children’s subsequent well-being. So his wanting that they should prosper cannot consist in his believing that he will be happy if/when they do, since he has no expectation of even being in existence in that eventuality. As Gosling puts it, there is a clear difference between thinking that something’s coming about will bring one pleasure, on the one hand, and viewing the prospect of its coming about with pleasure, on the other. (shrink)

Extant semantic theories for languages containing vague expressions violate intuition by delivering the same verdict on two principles of classical propositional logic: the law of noncontradiction and the law of excluded middle. Supervaluational treatments render both valid; many-Valued treatments, Neither. The core of this paper presents a natural deduction system, Sound and complete with respect to a 'mixed' semantics which validates the law of noncontradiction but not the law of excluded middle.

For the claim that the satisfaction of certain conditions is sufficient for the application of some concept to serve as part of the (‘reductive’) analysis of that concept, we require the conditions to be specified without employing that very concept. An account of the application conditions of a concept not meeting this requirement, we call analytically circular. For such a claim to be usable in determining the extension of the concept, however, such circularity may not matter, since if the concept (...) figures in a certain kind of intensional context in the specification of the conditions, the satisfaction of those conditions may not itself depend on the extension of the concept. We put this by saying that although analytically circular, the account may yet not be inferentially circular. (shrink)

A.N. Prior once showed that on certain apparently reasonable assumptions, a thesis sometimes associated with the name of Hume to the effect that no set of factual statements can ever entail an evaluative statement, is quite untenable. We assume only that there is at least one statement of each kind, and that the negation of a factual statement is factual — a principle we may call ‘N'. Now consider the disjunction F V E of some factual with some evaluative statement. (...) Since the disjunction is entailed by F, a factual statement, it must, if principle H is correct, be classified as factual. But by N, ∽ F is also factual, and this together with F V E entails E, thus violating H since E was exhypothesi an evaluative statement. (shrink)

The totality of extensional 1-ary connectives distinguishable in a logical framework allowing sequents with multiple or empty (alongside singleton) succedents form a lattice under a natural partial ordering relating one connective to another if all the inferential properties of the former are possessed by the latter. Here we give a complete description of that lattice; its Hasse diagram appears as Figure 1 in §2. Simple syntactic descriptions of the lattice elements are provided in §3; §§4 and 5 give some additional (...) remarks on matrix methods and on alternative terminology. Background: The size of this lattice was underestimated in [3]; some missing cases were noted in [4] in the course of correcting an example from [3] purporting to show the non-distributivity of the lattice. All the 'missing cases' (as well as those originally noted) are covered here. (The present discussion is self-contained.). (shrink)

We give in this paper a sufficient condition, cast in semantic terms, for Hallden-completeness in normal modal logics, a modal logic being said to be Hallden-complete (or Ήallden-reasonable') just in case for any disjunctive formula provable in the logic, where the disjuncts have no propositional variables in common, one or other of those disjuncts is provable in the logic.

An account of desire as a species of belief may owe its appeal to the details of its proposal as to precisely what sort of beliefs desires are to be identified with, and its downfall may be due to those details it does provide. For example, it may be proposed that the desire that α is in fact the belief that it ought to be that α, or is morally good or desirable that it should be the case that α. (...) Here the appeal might be that of forging a link between the holding of a moral belief and the acknowledgment that one has a reason for acting a certain way; and the shortcoming of the suggestion is its evident implausibility: even if the ‘necessity’ direction could be established, having a desire hardly seems sufficient for the holding of any such belief. Again: it might be proposed, perhaps simply to bring some order into the realm of propositional attitudes by reducing some to others, that the belief with which we should identify a’s desire that α is a’s belief that he will or would be happy if α. This proposed identification can be seen to be incorrect by consideration of examples such as the following, due to J. Gosling. An aging and ailing parent might forego numerous pleasures in order that his children should reap the benefits of his saving and have a good start in life – perhaps by receiving an expensive education – after his impending death. Oearly he may want that they should so benefit even if he does not believe in an after-death existence in which he might come to know of, and so take pleasure in, his children’s subsequent well-being. So his wanting that they should prosper cannot consist in his believing that he will be happy if/when they do, since he has no expectation of even being in existence in that eventuality. As Gosling puts it, there is a clear difference between thinking that something’s coming about will bring one pleasure, on the one hand, and viewing the prospect of its coming about with pleasure, on the other. (shrink)

Tarski 1968 makes a move in the course of providing an account of ?definitionally equivalent? classes of algebras with a businesslike lack of fanfare and commentary, the significance of which may accordingly be lost on the casual reader. In ?1 we present this move as a response to a certain difficulty in the received account of what it is to define a function symbol (or ?operation symbol?). This difficulty, which presents itself as a minor technicality needing to be got around (...) especially for the case of symbols for zero-place functions (for ?distinguished elements?), has repercussions?not widely recognised?for the account of functional completeness in sentential logic. A similarly stark comment in Church 1956 reveals an appreciation of this difficulty, though not every subsequent author on the topic has taken the point. We fill out this side of the picture in ?2. The discussion of functional completeness in ?2 is supplemented by some remarks on what is involved in defining a connective, which have been included in an Appendix. The emphasis throughout is on conceptual clarification rather than on proving theorems, and the main body of the paper may be regarded as an elaboration on the remarks just mentioned by Tarski and Church. The Appendix (?3) is intended to be similarly clarificatory, though this time with some corrective intent, of remarks made in and about Makinson 1973. (shrink)

SummaryIf you know you can recognise positive instances of a property, can you use this knowledge so as to be able to recognise also its negative instances? This is the question to be adressed.

A.N. Prior once showed that on certain apparently reasonable assumptions, a thesis sometimes associated with the name of Hume to the effect that no set of factual statements can ever entail an evaluative statement, is quite untenable. We assume only that there is at least one statement of each kind, and that the negation of a factual statement is factual — a principle we may call ‘N'. Now consider the disjunction F V E of some factual with some evaluative statement. (...) Since the disjunction is entailed by F, a factual statement, it must, if principle H is correct, be classified as factual. But by N, ∽ F is also factual, and this together with F V E entails E, thus violating H since E was exhypothesi an evaluative statement. (shrink)

An analogy between functional dependencies and implicational formulas of sentential logic has been discussed in the literature. We feel that a somewhat different connexion between dependency theory and sentential logic is suggested by the similarity between Armstrong's axioms for functional dependencies and Tarski's defining conditions for consequence relations, and we pursue aspects of this other analogy here for their theoretical interest. The analogy suggests, for example, a different semantic interpretation of consequence relations: instead of thinking ofB as a consequence of (...) a set of formulas {A1,...,A n} whenB is true on every assignment of truth-values on which eachA i is true, we can think of this relation as obtaining when every pair of truth-value assignments which give the same truth-values toA 1, the same truth-values toA 2,..., and the same truth-values toA n, also make the same assignment in respect ofB. We describe the former as the consequence relation inference-determined by the class of truth-value assignments (valuations) under consideration, and the latter as the consequence relation supervenience-determined by that class of assignments. Some comparisons will be made between these two notions. (shrink)

A purported axiomatization, by P. Gärdenfors, of intuitionistic propositional logic is shown to be incomplete, and that the mistaken claim to completeness is seen to result from carelessness in the choice of primitive logical vocabulary. This leads to a consideration of various ways of conceiving the distinction between primitive and defined vocabularies, along with the bearing of these differences on such matters as are discussed in connection with Gärdenfors.

The adverse reaction to Hempel's 'ravens paradox' embodied in giving it that description is compared with the usual reaction of experimental subjects to the Wason selection task.

We illustrate, with three examples, the interaction between boolean and modal connectives by looking at the role of truth-functional reasoning in the provision of completeness proofs for normal modal logics. The first example (§ 1) is of a logic (more accurately: range of logics) which is incomplete in the sense of being determined by no class of Kripke frames, where the incompleteness is entirely due to the lack of boolean negation amongst the underlying non-modal connectives. The second example (§ 2) (...) focusses on the breakdown, in the absence of boolean disjunction, of the usual canonical model argument for the logic of dense Kripke frames, though a proof of incompleteness with respect to the Kripke semantics is not offered. An alternative semantic account is developed, in terms of which a completeness proof can be given, and this is used (§ 3) in the discussion of the third example, a bimodal logic which is, as with the first example, provably incomplete in terms of the Kripke semantics, the incompleteness being due to the lack of disjunction (as a primitive or defined boolean connective). (shrink)

If what is known need not be closed under logical consequence, then a distinction arises between something's being known to be the case (by a specific agent) and its following from something known (to that subject). When each of these notions is represented by a sentence operator, we get a bimodal logic in which to explore the relations between the two notions.