Logical Necessity

The paper argues against Bob Hale's (1999) argument that enquirers must regard some truths as necessary truths. Hale's argument against Quinean skepticism. like many similar arguments due to McFetridge, Wright and others, involves a quantifier shift fallacy.

It is usually held that what distinguishes a good inference from a bad one is that the former is but the latter is not truth-preserving. What is behind this view is the basic assumption that whether a certain inference is truth-preserving or not is a genuine issue, an issue the answer to which is determined objectively. This view is called the realist view of logic. ;In this dissertation the realist view of logic is criticized and an alternative view is presented. (...) The alternative is called the fictionalist view of logic. On this view, what makes a logical system good is not that its inferential rules are truth-preserving, but rather that it has a certain proof-theoretic property, called deductive conservativeness. More specifically, it is argued that if the inferential rules for the logical operators involved in the system are conservative over the deductive system which is devoid of logical operators, then the conservative system will have all the virtues we expect in a good logical system. It is shown however that insofar as the system is conservative, there is no way to determine whether its inferential rules are truth-preserving or not; thus the latter is simply irrelevant to the goodness of the logical system. To support this claim, the view that the meaning of a logical operator is determined not by its semantic properties such as truth but by its inferential role, is advocated. A significant implication of this view is that there is no answer to the question which of the conservative logical systems is the correct logic for the world. ;Furthermore, it is maintained that metalogical claims of implication and consistency, namely claims of the forms 'A implies B', and 'A is consistent', can be taken as modal claims which involve modal operators as logical operators, and thus the above approach is applicable to such metalogical claims, too. This idea is used to avoid our ontological commitment to mathematical entities such as models and proofs employed in metalogic. (shrink)

In this paper the logic of broad necessity is explored. Definitions of what it means for one modality to be broader than another are formulated, and it is proven, in the context of higher-order logic, that there is a broadest necessity, settling one of the central questions of this investigation. It is shown, moreover, that it is possible to give a reductive analysis of this necessity in extensional language. This relates more generally to a conjecture that it is not possible (...) to define intensional connectives from extensional notions. This conjecture is formulated precisely in higher-order logic, and concrete cases in which it fails are examined. The paper ends with a discussion of the logic of broad necessity. It is shown that the logic of broad necessity is a normal modal logic between S4 and Triv, and that it is consistent with a natural axiomatic system of higher-order logic that it is exactly S4. Some philosophical reasons to think that the logic of broad necessity does not include the S5 principle are given. (shrink)

I show that intuitive and logical considerations do not justify introducing Leibniz’s Law of the Indiscernibility of Identicals in more than a limited form, as applying to atomic formulas. Once this is accepted, it follows that Leibniz’s Law generalises to all formulas of the first-order Predicate Calculus but not to modal formulas. Among other things, identity turns out to be logically contingent.

In these few pages I shall try to demonstrate the emptiness of the most cumbersome piece of unexamined intellectual baggage at present being hauled about by English philosophers. I here cite one example to be going on with, at the end of the paper I shall give a handful more, and it would be easy to multiply the number by ten from the writings of reputable philosophers. The outstanding philosophical achievement of the ha1f-century which has just drawn to a close (...) [i.e. the period 1900-1950] has been an appreciation of the peculiar status of a priori judgments and of logically necessary or formally true propositions. . . . Though many problems remain unsolved, the main outline is now clear: formally true statements assert nothing about the world; instead, their function is to state principles according to which empirical propositions are deduced from other empirical propositions . . . (R. B. Braithwaite, ‘Moral Principles and Inductive Policies’, Proceedings of the British Academy 1950). What is wrong with this passage and with the myth of which it is an expression is its assumption that we have clear notions of what it is for a proposition to be logically necessary and of what it is for a proposition to assert something about the world, these notions being such that it is plausible to say that it has recently been discovered that every proposition having the first of these properties lacks the second. This assumption is wrong: there is no body of published theory giving a clear account of such notions, and despite fairly diligent searching I have so far failed to find, among the many philosophers who accept the myth, one who is able when challenged to supplement the literature on this vital point. Let me make it clear at once that I am not going to defend synthetic a priori truths - I am going to attack a popular mishandling of the truth that all necessary truths are analytic, and through this attack to draw right-wing conclusions from left-wing premisses.. (shrink)

I propose a comprehensive account of negation as a modal operator, vindicating a moderate logical pluralism. Negation is taken as a quantifier on worlds, restricted by an accessibility relation encoding the basic concept of compatibility. This latter captures the core meaning of the operator. While some candidate negations are then ruled out as violating plausible constraints on compatibility, different specifications of the notion of world support different logical conducts for negations. The approach unifies in a philosophically motivated picture the following (...) results: nothing can be called a negation properly if it does not satisfy Contraposition and Double Negation Introduction; the pair consisting of two split or Galois negations encodes a distinction without a difference; some paraconsistent negations also fail to count as real negations, but others may; intuitionistic negation qualifies as real negation, and classical Boolean negation does as well, to the extent that constructivist and paraconsistent doubts on it do not turn on the basic concept of compatibility but rather on the interpretation of worlds. (shrink)

In this paper I offer a straight solution to Hume's problem of induction by defusing the assumptions on which it is based. I argue that Hume's problem only arises if we accept (i) that there is no necessity but logical necessity, or (ii) that it is unreasonable to believe that there is any form of necessity in addition to logical necessity. I show that Hume's arguments in favour of (i) and (ii) are unsound. I then offer a suggestion as to (...) how the weakness of his arguments has escaped detection. Finally, having claimed that there remains a surmountable problem with inductive arguments, I end by characterising that problem and a possible approach to its solution. (shrink)

Which mathematical structures are possible, that is, instantiated by the concrete inhabitants of some possible world? Are there worlds with four-dimensional space? With infinite-dimensional space? Whence comes our knowledge of the possibility of structures? In this paper, I develop and defend a principle of plenitude according to which any mathematically natural generalization of possible structure is itself possible. I motivate the principle pragmatically by way of the role that logical possibility plays in our inquiry into the world.

In sections 1 through 5, I develop in detail what I call the standard theory of worlds and propositions, and I discuss a number of purported objections. The theory consists of five theses. The first two theses, presented in section 1, assert that the propositions form a Boolean algebra with respect to implication, and that the algebra is complete, respectively. In section 2, I introduce the notion of logical space: it is a field of sets that represents the propositional structure (...) and whose space consists of all and only the worlds. The next three theses, presented in sections 3, 4, and 5, respectively, guarantee the existence of logical space, and further constrain its structure. The third thesis asserts that the set of propositions true at any world is maximal consistent; the fourth thesis that any two worlds are separated by a proposition; the fifth thesis that only one proposition is false at every world. In sections 6 through 10, I turn to the problem of reduction. In sections 6 and 7, I show how the standard theory can be used to support either a reduction of worlds to propositions or a reduction of propositions to worlds. A number of proposition-based theories are developed in section 6, and compared with Adams's world-story theory. A world-based theory is developed in section?, and Stalnaker's account of the matter is discussed. Before passing judgment on the proposition based and world-based theories, I ask in sections 8 and 9 whether both worlds and propositions might be reduced to something else. In section 8, I consider reductions to linguistic entities; in section 9, reductions to unfounded sets. After rejecting the possibility of eliminating both worlds and propositions, I return in section 10 to the possibility of eliminating one in favor of the other. I conclude, somewhat tentatively, that neither worlds nor propositions should be reduced one to the other, that both worlds and propositions should be taken as basic to our ontology. (shrink)

Recently it has become almost the received wisdom in certain quarters that Kripke models are appropriate only for something like metaphysical modalities, and not for logical modalities. Here the line of thought leading to Kripke models, and reasons why they are no less appropriate for logical than for other modalities, are explained. It is also indicated where the fallacy in the argument leading to the contrary conclusion lies. The lessons learned are then applied to the question of the status of (...) the formula. (shrink)

One skeptical strategy against A’s claim to know that P is to hold that it is logically possible for someone to have the same “base” for P as A does in spite of its not being true that P. Philosophical replies have focussed on showing that these are not genuine possibilities. Whether they are can be an interesting question of metaphysics, but it is argued in this paper that this metaphysical discussion is not the proper focus for an assessment of (...) skepticism. Even if there are the odd logical possibilities, they do not suffice to warrant skeptical doubts. Rather, there has to be good reason to think that there is a genuine chance of the alleged possibility obtaining. This requirement cannot be satisfied generically, and that is what is wrong with generic skepticism. (shrink)

This paper aims to explain how the Tractatus attempts to unify logic by deriving the truth-functionality of logical necessity from the thesis that a proposition shows its sense. I first interpret the Tractarian notion of showing as the displaying of what is intrinsic to an expression (or a symbol). Then I argue that, according to the Tractatus, the thesis that a proposition shows its sense implies the determinacy of sense, the possibility of the complete elimination of non-primitive symbols, the analyticity (...) thesis and the strong analyticity thesis. The picture theory emerges as what provides the only acceptable account of an elementary proposition, subject to the constraint that a proposition must show its sense. The picture theory and the analyticity thesis then entail the contingency thesis (that an elementary proposition is contingent) and the independence thesis (that elementary propositions are mutually logically independent) which, together with the strong analyticity thesis, imply that all logical propositions are tautologies. (shrink)

One of the most basic methods of philosophy is, and has always been, the consideration of counterfactual cases and imaginary scenarios. One purpose of doing so obviously is to test our theories against such counterfactual cases. Although this method is widespread, it is far from being commonly accepted. Especially during the last two decades it has been confronted with criticism ranging from complete dismissal to denying only its critical powers to a cautious defense of the use of thought experiments as (...) counterexamples. One of the strongest criticisms of the method of thought experimentation is "modal skepticism" as explicated and defended by Peter van Inwagen. Van Inwagen argues that the philosopher's notion of logical possibility is confused and that its epistemology is dubious. I argue that van Inwagen's skepticism is unwarranted. There is a sufficiently clear notion of logical possibility and a sufficiently straightforward way of getting to know what is logically possible. In the remainder of the paper I show how that connects with the methodology of thought experimentation in philosophy. (shrink)

HUME AND HIS FOLLOWERS HAVE TRIED UNSUCCESSFULLY TO ESTABLISH THE IMPOSSIBILITY OF MIRACLES BY APPEALING SOLELY TO THE DEFINITIONS OF MIRACLE AND NATURAL LAW. HUME’S ARGUMENT TRADES UPON THAT PART OF THE DEFINITION OF MIRACLE WHICH PERTAINS TO THE NUMERICAL INSIGNIFICANCE OF MIRACULOUS EVENTS. HE DID NOT REALIZE THAT THE LARGE NUMERICAL DIFFERENCE BETWEEN NON-REPEATABLE IRREGULAR EVENTS AND REPEATABLE REGULAR ONES LOGICALLY CANNOT BE USED AS A CRITERION BY WHICH TO DETERMINE THE EXISTENTIAL STATUS OF NUMERICALLY SMALL NON-REPEATABLE IRREGULAR EVENTS. (...) USING A SIMILAR STRATEGY, THE CONTEMPORARY HUMEAN APPEALS TO PART OF THE DEFINITION OF NATURAL LAW, TO THE IDEA OF ITS ESSENTIAL GENERALITY. WHETHER "ESSENTIALLY GENERAL" IS TAKEN TO MEAN AN INTRINSIC NATURAL NECESSITY OR A NECESSITY IMPUTED TO NATURE, IN NEITHER CASE CAN THE LOGICAL IMPOSSIBILITY OF MIRACLES BE ESTABLISHED. (shrink)

In his influential paper ‘‘Essence and Modality’’, Kit Fine argues that no account of essence framed in terms of metaphysical necessity is possible, and that it is rather metaphysical necessity which is to be understood in terms of essence. On his account, the concept of essence is primitive, and for a proposition to be metaphysically necessary is for it to be true in virtue of the nature of all things. Fine also proposes a reduction of conceptual and logical necessity in (...) the same vein: a conceptual necessity is a proposition true in virtue of the nature of all concepts, and a logical necessity a proposition true in virtue of the nature of all logical concepts. I argue that the plausibility of Fine's view crucially requires that certain apparent explanatory links between essentialist facts be admitted and accounted for, and I make a suggestion about how this can be done. I then argue against the reductions of conceptual and logical necessity proposed by Fine and suggest alternative reductions, which remain nevertheless Finean in spirit. (shrink)

Interest in the metaphysics and logic of possible worlds goes back at least as far as Aristotle, but few books address the history of these important concepts. This volume offers new essays on the theories about the logical modalities held by leading philosophers from Aristotle in ancient Greece to Rudolf Carnap in the twentieth century. The story begins with an illuminating discussion of Aristotle's views on the connection between logic and metaphysics, continues through the Stoic and mediaeval traditions, and then (...) moves to the early modern period with particular attention to Locke and Leibniz. The views of Kant, Peirce, C. I. Lewis and Carnap complete the volume. Many of the essays illuminate the connection between the historical figures studied, and recent or current work in the philosophy of modality. The result is a rich and wide-ranging picture of the history of the logical modalities. (shrink)

This dissertation is divided into three parts. The first part consists of a detailed descriptive summary of the interpretive commentaries following the publication of Wittgenstein's Remarks on the Foundation of Mathematics. The material, thus assembled and presented as a whole for the first time, reveals unities directly traceable to assumptions and issues introduced by one man, Michael Dummett, who gave the interpretive literature its impetus, form and substance. ;The second part of the dissertation is of a critical nature. In this (...) part it will be shown that Dummett's interpretation and assessment of Wittgenstein's philosophical activities is inadequate. Dummett's requirements for solving the problem of logical necessity require contradictory things of Wittgenstein. Further, the criteria which Dummett uses to judge the success of Wittgenstein's efforts are the very criteria which Wittgenstein attacks successfully in the Remarks. ;Having shown that the literature depends heavily on Dummett, and that Dummett is fundamentally mistaken, the third and remaining part of the dissertation attempts an expository sketch in which Wittgenstein's thoughts on logical necessity are provided. This sketch attempts to avoid the pitfalls of Dummett's approach and preserve Wittgenstein's avoidance of philosophical theorizing. (shrink)

McFetridge (in Logical necessity and other essays . London: Blackwell, 1990 ) suggests that to treat a proposition as logically necessary—to believe a proposition logically necessary, and to manifest that belief—is a matter of preparedness to deploy that proposition as a premise in reasoning from any supposition. We consider whether a suggestion in that spirit can be generalized to cover all cases of absolute necessity, both logical and non-logical, and we conclude that it can. In Sect. 2, we explain the (...) significance that such an account of manifestation of belief in absolute necessity has for the prospects of a non-realist theory of modality. In Sect. 3, we offer a sympathetic articulation of the detail that underlies the McFetridge conception of belief in logical necessity. In Sects. 4 and 5, we show that the conception so articulated will not generalize to encompass all cases of belief in absolute necessity and proceed to offer a remedy. Our proposal is based upon a distinction between two kinds of suppositional act: A-supposing and C-supposing (Sect. 6). In Sect. 7, we then explain and defend our central thesis: (roughly) that (manifestation of) belief in absolute necessity is a matter of preparedness to deploy as a premise in reasoning under any C-supposition. Finally, we indicate that there is some promise in the parallel thesis that manifestation of the treatment of a proposition as a priori is a matter of preparedness to deploy as a premise in reasoning under any A-supposition (Sect. 8). (shrink)

Kripke and putnam have argued that metaphysical necessity is truth in all possible worlds, Hence is a kind of logica necessity; it is this claim I argue against. My argument proceeds by way of my considering and elaborating an example to show that although 'gold has atomic number 79' be counted a metaphysically necessary truth, There is a possible world in which it is false; it turns out to be for all I show here at most a physical necessity, True (...) in all those worlds structurally similar to the actual world. (shrink)

The following questions are discussed here. Is induction a reasonable procedure in the context of a denial of physically necessary connections? What is physical necessity? If induction does presuppose physical necessity, what amount of it is presupposed? It is argued that with logic as the only restriction on what is to count as a possible world, it is unreasonable to claim that observed connections, whether universal or statistical, will continue to hold. The concept of physical necessity is no more problematic (...) than that of logical necessity, once it is recognized that the necessity of physical and logical necessity is the same. A variant of Keynes' principle of limited independent variety answers the question of the amount of physical necessity presupposed. (shrink)

Modal Platonism utilizes "weak" logical possibility, such that it is logically possible there are abstract entities, and logically possible there are none. Modal Platonism also utilizes a non-indexical actuality operator. Modal Platonism is the EASY WAY, neither reductionist nor eliminativist, but embracing the Platonistic language of abstract entities while eliminating ontological commitment to them. Statement of Modal Platonism. Any consistent statement B ontologically committed to abstract entities may be replaced by an empirically equivalent modalization, MOD(B), not so ontologically committed. This (...) equivalence is provable using Modal/Actuality Logic S5@. Let MAX be a strong set theory with individuals. Then the following Schematic Bombshell Result (SBR) can be shown: MAX logically yields [T is true if and only if MOD(T) is true], for scientific theories T. The proof utilizes Stephen Neale's clever model-theoretic interpretation of Quantified Lewis S5, which I extend to S5@. (shrink)

Speech given by Markus Gabriel within the international meeting “Presente del idealismo alemán” organized by the Philosophy Department of the Universidad Nacional de Colombia. This conference was held on October 9, 2009.

Graham Oppy has argued that possible explanation entails explanation in order to object to Richard Gale and Alexander Pruss’s new cosmological argument that it does not improve upon familiar cosmological arguments. Gale and Pruss as well as Pruss individually have granted Oppy’s inference from possible explanation to explanation and argue that this inference provides a reason to believe that the strong principle of sufficient reason is true. In this article, I shall undermine Oppy’s objection to the new cosmological argument by (...) arguing that it is logically possible that some truths are merely possibly explained. (shrink)

I investigate two asymmetrical approaches to knowledge of absolute possibility and of necessity--one which treats knowledge of possibility as more fundamental, the other according epistemological priority to necessity. Two necessary conditions for the success of an asymmetrical approach are proposed. I argue that a possibility-based approach seems unable to meet my second condition, but that on certain assumptions--including, pivotally, the assumption that logical and conceptual necessities, while absolute, do not exhaust the class of absolute necessities--a necessity-based approach may be able (...) to do so. (shrink)

Must we believe in logical necessity? I examine an argument for an affirmative answer given by Ian McFetridge in his posthumously published paper 'Logical Necessity: Some Issues', and explain why it fails, as it stands, to establish his conclusion. I contend, however, that McFetridge's argument can be effectively buttressed by drawing upon another argument aimed at establishing that we ought to believe that some propositions are logically necessary, given by Crispin Wright in his paper 'Inventing Logical necessity'. My contention is (...) that Wright's argument, whilst it likewise fails, as it stands, to establish the necessity of necessity, established enough to close off what appears to me to be the only effective-looking sceptical response to McFetridge's original argument. My paper falls into four principal parts. In the first I expound McFetridge's argument and draw attention to the possibility of a certain type of sceptical counter to it. In the second, I begin a response to this sceptical move, taking it as far as I can without reliance upon argument of the kind given by Wright. Turning, then, to Wright's argument, I explain to what extent I think it is successful and seek to rebut some objections to the argument which, were they well-taken, would show that the argument cannot enjoy even the partial success I which to claim for it. Finally, I return to my main theme and try to show, with the assistance of what I take to be solidly established by Wright's argument, that the sceptical response collapses. (shrink)

The philosophy of modality investigates necessity and possibility, and related notions--are they objective features of mind-independent reality? If so, are they irreducible, or can modal facts be explained in other terms? This volume presents new work on modality by established leaders in the field and by up-and-coming philosophers. Between them, the papers address fundamental questions concerning realism and anti-realism about modality, the nature and basis of facts about what is possible and what is necessary, the nature of modal knowledge, modal (...) logic and its relations to necessary existence and to counterfactual reasoning. The general introduction locates the individual contributions in the wider context of the contemporary discussion of the metaphysics and epistemology of modality. (shrink)

It may sometimes be useful in philosophy to state a method of argument in very simple and even over-simplified terms; it may at a certain stage be useful to ignore for the moment the details and difficulties of particular philosophical arguments, and to try to state simply what is commonly assumed in a variety of different and even opposing arguments.

The problem of the source of necessity is the problem of explaining what makes necessary truths necessarily true. Simon Blackburn has presented a dilemma intended to show that any reductive, realist account of the source of necessity is bound to fail. Although Blackburn's dilemma faces serious problems, reflection on the form of explanations of necessities reveals that a revised dilemma succeeds in defeating any reductive account of the source of necessity. The lesson is that necessity is metaphysically primitive and irreducible.