Computer Laboratory

Technical reports

The temporal properties of English conditionals and modals

Richard Crouch

January 1994, 248 pages

This technical report is based on a dissertation submitted April 1993 by the author for the degree of Doctor of Philosophy to the University of Cambridge.


This thesis deals with the patterns of temporal reference exhibited by conditional and modal sentences in English, and specifically with the way that past and present tenses can undergo deictic shift in these contexts. This shifting behaviour has consequences both for the semantics of tense and for the semantics of conditionals and modality.

Asymmetries in the behaviour of the past and present tenses under deictic shift are explained by positing a primary and secondary deictic centre for tenses. The two deictic centres, the assertion time and the verification time, are given independent motivation through an information based view of tense. This holds that the tense system not only serves to describe the way that the world changes over time, but also the way that information about the world changes. Information change takes place in two stages. First, it is asserted that some fact holds. And then, either at the same time or later, it is verified that is assertion is correct.

Typically, assertion and verification occur simultaneously, and most sentences convey verified information. Modals and conditionals allow delayed assertion and verification. “If A, then B” means roughly: suppose you were now to assert A; if and when A is verified, you will be in a position to assert B, and in due course this assertion will also be verified. Since A and B will both be tensed clauses, the shifting of the primary and secondary deictic centres leads to shifted interpretations of the two clauses.

The thesis presents a range of temporal properties of indicative and subjunctive conditionals that have not previously been discussed, and shows how they can be explained. A logic is presented for indicative conditionals, based around an extension of intuitionistic logic to allow for both verified and unverified assertions. This logic naturally gives rise to three forms of epistemic modality, corresponding to “must”, “may” and “will”.

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BibTeX record

  author =	 {Crouch, Richard},
  title = 	 {{The temporal properties of English conditionals and modals}},
  year = 	 1994,
  month = 	 jan,
  url = 	 {},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-325}