Abstract

The last chapter examines the tense system used by ordinarily competent speakers of English to discuss past, present, and future events, actual and possible events, and various combinations of these. I present a systematic method for translating English sentences containing certain compound verb tenses and embedded tense constructions into a logical language using tense operators. Finally I show how the usual semantics for these operators reflects the truth conditions of the original English sentences. I argue, however, that a tense logical semantics reflecting the use of tense in English will contain a partially ordered tense structure rather than one that is linearly ordered or branching. ;The third chapter discusses logic of 'unless'. I show that many of the previously puzzling features of this word can be understood by considering the tenses of the verbs in the sentences joined by 'unless'. In a number of cases it turns out that 'unless' should not be interpreted as a truth-functional connective at all, but is best understood as an intensional, tense connective. ;In the second chapter I discuss Quine's doctrine of eternal sentences. I take Quine's position to be that all the information important for logic and science presented in tensed English sentences can also be presented by eternal sentences which use timeless verbs and data and clock times. I argue that in so far as logic and science are concerned with an analysis of the reasons for human action, and with the explanation and prediction of specific events, eternal sentences lose indexical information that is necessary to accomplish these tasks. ;The first chapter investigates what may be called the standard view of propositions. On this view propositions are abstract objects that are timelessly true , and serve both as the meanings of sentences and as the objects of propositional attitudes. Although this view was widely held by a previous generation of logicians and is found in many textbooks today, there are serious difficulties in the view. I show that many of these difficulties stem from the claim that propositions are timelessly true . The standard view has been revised in two general ways. The first sort of revision allows propositions to be sometimes true and sometimes false. This position is consistent with the development of tense logic as one of the intensional logics. The second sort of revision replaces the notion of timeless propositions with that of eternal sentences which always have the same truth value. On this view tense logic is not worth serious philosophic attention since its basic notion, that of truth at a time, can be eliminated in favor of eternal truth. ;The first part of the project examines two major sources of criticism of tense logic: the view that logic is concerned with timeless propositions, and Quine's doctrine of eternal sentences. The second part of the project discusses several problems in logical theory that the use of tense logic can clarify or resolve, and that alternative theories are unable to present accurately, much less to elucidate. ;In the past few years there has been increasing interest in the logic of indexicals, including the temporal indexical 'now', and in the relationship between tense and modality. Although modern tense logic has reached a high level of technical sophistication, often specifically in response to this interest, many philosophers remain skeptical about the value of tense logic as a philosophic tool. This thesis addresses that skepticism and argues that it is unjustified