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The Structure and Ontology of Logical Space June 1983

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The Structure and Ontology of Logical Space June 1983 WORLDS AND PROPOSITIONS: The Structure and Ontology of Logical Space Phillip Bricker A DISSERTATION PRESENTED TO THE FACULTY OF PRINCETON UNIVERSITY IN CANDIDACY FOR THE DEGREE OF DOCTOR OF PH I LOSOPHY RECOMMENDED FOR ACCEPTANCE BY THE DEPARTMENT OF PHILOSOPHY June 1983 © 1983 Phillip Bricker ALL RIGHTS RESERVED ACKNOWLEDGMENTS I acknowledge with pleasure an enormous intellectual debt to my thesis adviser, David Lewis, both for his extensive and invaluable comments on various drafts of this work, and, more generally, for teaching me so much of what I know about matters philosophical. CONTENTS Introduction. 3 Section 1: Propositions and Boolean Algebra. 10 First Thesis. 10 First Reformulation: The Laws of Propositional Logic. 15 Second Reformulation: The Lindenbaum-Tarski Algebra. 21 Objections to the First Thesis. 28 Second Thesis. 33 Objections to the Second Thesis. 3& section 2: Logical Space. 38 Logical Space as a Field of Sets. 38 Alternative Conceptions of Logical Space. 44 section 3: Maximal Consistent Sets of Propositions. 48 Third Thesis. 48 Atomic Propositions. 52 Finite Consistency. 55 Objections to the Third Thesis. 59 section 4: Separating Worlds by Propositions. 68 Fourth Thesis. 68 Indiscernibility Principles. 71 Objections to the Fourth Thesis. 74 Section 5: Consistency and Realizability. 78 Fifth Thesis. 78 The Compact Theory. 82 The Mathematical Objection. 91 The Modal Objection. 105 Section 6: Proposition-Based Theories. 117 Tripartite Correspondence. 117 Weak and Feeble Proposition-Based Theories. 123 Adams's World-Story Theory. 131 Section 7: The World-Based Theory. 138 Isomorphic Algebras. 138 Stalnaker on Adams. 148 Section 8: Reducing possible Worlds to Language. 156 Introduction. 156 Three Necessary Conditions for Reduction. 161 First Proposal. 170 The Circularity Objection. 172 The Cardinality Objection. 174 Second Proposal. 180 Further Generalizations. 187 The Objection from Descriptive Impoverishment. 189 The Fallback Position: Carnap's Proposal. 194 Section 9: The Disappearance Theory. 200 Section 10: Proposition-Based Vs. World-Based Theories. 208 Introduction. 208 Reduction, Realism, and Pragmatism. 209 The Pragmatic Approach. 219 Against the Proposition-Based Theory. 220 Against the World-Based Theory. 229 Appendices. 235 First Appendix. 235 Second Appendix. 238 List of Principal Theses and Definitions. 243 Bibliography. 246 ABSTRACT 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 I, 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 - 1 - 2 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. INTRODUCTION I take it that propositions and possible worlds will have a role to play in any systematic reconstruction of our conceptual scheme. That is not to say, however, that one must be a realist with respect to propositions and possible worlds, that one must take propositions and possible worlds as basic to one's ontology. Perhaps both propositions and possible worlds can be reduced to entities considered ontologically more respectable. Or, failing this, perhaps the ontologically less respectable of the two can be reduced to the other. These questions of reduction will be the chief concern of the latter half of this work, sections 6 through 10. Such questions can only be answered relative to a specification of the theory of propositions and possible worlds that a reduction would be required to preserve. To this end, I develop in the first half of this work, sections 1 through 5, what I call the standard theory of propositions and possible worlds, and I examine some of the theory's metaphysical implications. Before turning to this theory, however, I need to make some preliminary remarks about the notion of proposition with Vlhich the theory is concerned. What I mean by the term 'proposition' is to be taken from the theses I explicitly adopt, not from whatever preconceived notions one may have about the term. But I have not shied aVlay from using an old, imprecise - 3 - 4 term to designate a more precise, even technical concept, so as not to lose sight of how that, concept roughly fits into the general scheme of things: understanding is not fostered in a vacuum. Whoever appropriates an old term in this way has the responsibility of making clear just which of the old senses he is trying to explicate, so that there will be no confusion as to what is not meant by the term. With 'proposition' the problem is especially acute. The term has been used in so many different ways throughout its checkered career that it is multiply ambiguous, and in a devious way that has often gone unrecognized. 1 No wonder, since for most practical purposes, and many philosophical ones, the different senses need not be distinguished; to do so would be tedious: But undergoing some such tedium would be well- advised for the philosophical task I have before me, lest I be accused of equivocating in a place where it matters. First, let me set aside some conceptions of proposition that will not be invoked in this work. Propositions have sometimes been identified with sentences, either interpreted or uninterpreted, either tokens or types. On the present conception, I will say that propositions are expressed by sentences, but the propositions are to be kept distinct from the sentences that express them. 2 Are all propositions expressed by 1 Fora short history of uses of the term 'proposition', see Alonzo Church, The Problem of Universals (Notre Dame, Ind.: University of Notre Dame Press, 1956), pp. 3-11. 2 Actually, such talk of sentences expressing propositions must be taken with a grain of salt. Most (if not all) sentences of a natural language only express propositions, in my sense, relative to a context of utterance, and even then, only if all vagueness and ambiguity has been eliminated. 5 the sentences of anyone language? Not for anything ordinarily called a language: there will not be enough sentences to do the job. 3 Propositions have sometimes been identified with ideas in the mind, or with other mental entities. On the present conception, these mental entities at most represent propositions; and I know of no reason for believing that any mind that ever was or will be is capable of representing all the propositions. Moreover, I will argue in sections 5 and 8 that propositions, in my sense, cannot be reduced to linguistic entities or to mental entities, in other words, that propositions cannot be constructed out of such entities. In this sense, propositions are independent of language and of thought. Propositions have sometimes been identified with the meanings of sentences, or of declarative sentences. I will call such a conception of proposition a semantic conception; there are as many semantic conceptions as there are ways of individuating meanings. I take it that propositions on a semantic conception have some sort of grammatical structure, perhaps the surface grammatical structure of the sentences that express them, perhaps some hypothetical deep structure or logical form. In any case, propositions of a semantic variety might differ because they differ in structure, even though they agree in factual content. 3 See sections 1 and 8 for relevant arguments. 6 That does not happen on what I will call a metaphysical conception of proposition, the sort of conception here being invoked. On a metaphysical conception, propositions are individuated solely by factual content, not by structure or form: 4 distinct propositions always differ in factual content. There are as many metaphysical conceptions of proposition as there are ways of explicating the notion of factual content. I can say something about the notion of factual content that I have in mind by relating propositions to possible worlds. Propositions are linked to worlds via a binary relation of truth: I will say that a proposition is true at a world. 5 I will also say that a proposition characterizes or describes any world at which it is true. In brief: propositions are properties of worlds. This excludes from consideration those conceptions according to which propositions only characterize worlds relative to something else, such as a time or a place.
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