Autumn 2011

27 Sept: Talk by Sara Uckelman, DZ5

Medieval Logic and Modern Logic: The Role and Process of Formalization

The High Middle Ages (13th-15th C) were a time of significant innovation in logic and philosophy of language. Unlike modern logic, which is done in symbolic notation, medieval logic was conducted via natural language (Latin) alone, and as a result medieval texts on logic can often be ambiguous and not as rigorous as a modern logician would like. Through the process of formalization, which involves tools from logic, computer science, argumentation theory, and artificial intelligence, the contemporary scholar can provide precise formal models of medieval logical texts, so that the content of the medieval texts can be clarified and made precise. The utility of the formal model goes in both directions; on the one hand, it allows us to see to what extent the medieval logical developments follow or foreshadowed modern developments in logic and formal semantics, and on the other hand, it makes accessible solutions that may be relevant to particular problems in modern logic and philosophy that are new and innovative.

In this talk we will discuss the role and process of formalization in understanding medieval logic, using as a case study the medieval theory of obligationes, a type of logical disputation between an Opponent and a Respondent which was extensively investigated in the 13th and 14th centuries.

11 Oct: Talk by Stefan Wintein, DZ6

Playing with Truth

In this talk, I present a snapshot of my PhD thesis Playing with Truth, which is a collection of papers that revolve around a single topic: that of self-referential truth. The talk will focus on the joint rationale of the three frameworks for truth that are developed in the thesis, which are:

  • Assertoric semantics.
  • The method of closure games.
  • The strict-tolerant calculus.

Assertoric semantics and the method of closure games are semantic valuation tools that are used to define theories of truth. The strict-tolerant calculus is a signed tableau calculus that can be used to obtain syntactic characterizations of various consequence relations that are induced by those theories. Assertoric semantics can be understood as a semantic counterpart of the strict-tolerant calculus and the method of closure games as a refinement of assertoric semantics. In a sense then, all three frameworks have a ”tableau-like” character. In each of our frameworks, the (tableau-like) rules, including those of the truth predicate, are interpreted as assertoric rules, whereas the (tableau-like) closure conditions are interpreted as assertoric norms, i.e., as norms that govern the practice of asserting and denying. In a nutshell, the three frameworks echo the assertoric conception of truth that I develop in my thesis. In the talk, we will articulate the relations between the three frameworks and the main results pertaining to them. However, the focus will be on applications of the frameworks.
In particular, we will illustrate how:

  • Assertoric semantics can be used to argue for the claim that self-referential truth has computational power.
  • Assertoric semantics and the strict-tolerant calculus jointly shed light on the strict-tolerant conception of truth, which is a novel conception of truth that has recently been proposed in joint work of Cobreros, Egré, Ripley and van Rooij.

1 Nov: Talk by Soroush Rafiee Rad, DZ4

Logic of Uncertain Public Announcements

Logics of Public announcement are the simplest forms of dynamic epistemic logics. These logics are developed to study the effect of public announcements in a group on the epistemic state of the group members. One underlying idealization that is present through out the literature, however, is the assumption that all announcements are honest and trustworthy.

The goal of this study is to generalize these logics to include as epistemic actions, announcements from untrustworthy sources or sources with less than complete reliability. A more interesting case is when each source of public announcement comes with a trust profile which identifies the epistemic character of the source for each group member. In particular a source of announcement can be considered trustworthy by one group member and uncertain or untrustworthy by another.

We shall generalize PAL to include as epistemic actions, announcements from three type of sources—trustworthy, uncertain and untrustworthy. In the next step we shall associate with each source of announcement a trust profile which identifies which of the three categorizes of trust is assigned to this source by each member.

8 Nov: Talk by Filip Buekens, DZ6

The Origin of Institutions: Grice or Searle

According to John Searle, institutional reality begins with Declaratives that create institutions, which, in turn, allow for the creation and maintanance of instititutional facts. One problem with this approach is that it becomes difficult to relate institutional reality with its evolutionary ancestors. How did territory behaviour in animals give rise to borders and property? In this talk I sketch an alternative to Searle’s approach, based on and very much inspired by the way Paul Grice sketches the emergence of conventional non-natural meaning. The upshot of the discussion is that a key distinction — that between regulative
rules and constitutive rules — is less relevant in a theory of institutions than Searle suggests.

6 Dec: Talk by Kristina Liefke,
DZ5 (rescheduled)

A Single-type Semantics for Natural Language

Richard Montague’s Intensional Logic [2] constitutes a milestone in the project of providing a formal semantics for natural language. Its use enables the systematic translation of natural into formal language expressions and allows a mathematically rigorous account of a wide range of semantic phenomena. Despite its success, Montague’s logic has, in the last decade, been subject to significant criticism [1, 3]. The latter pertains to the descriptive inadequacy of its underlying system of semantic domains, especially of the distinction between the interpretive domains of noun phrases (i.e. individuals) and sentences (i.e. propositions). To remedy this inadequacy, I develop a semantics for natural language that replaces individuals and propositions by a single type of object (hence ‘single-type semantics’). In particular, I compare different single-type alternatives, identify the most suitable candidate, and show that it models a standard fragment of English.

References

[1] Andrew Carstairs-McCarthy, The Distinction Between Sentences and Noun Phrases: An Impediment to Language Evolution? (Chris Knight, Michael Studdert-Kennedy, and James R. Hurford, eds.), Cambridge University Press, Cambridge and New York, 2000, 2000, pp. 248-263.

[2]Richard Montague, The Proper Treatment of Quantification in Ordinary English, Formal Philosophy: Selected Papers of Richard Montague (Richmond H. Thomason, ed.), Yale University Press, New Haven and London, 1976, 1973.

[3] Barbara H. Partee, Do We Need Two Basic Types?, 40-60 Puzzles for Manfred Krifka (Hans-Martin Gaertner, ed.), Berlin, 2006.

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