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  1. A State-of-Affairs-Semantic Solution to the Problem of Extensionality in Free Logic.Hans-Peter Leeb - 2020 - Journal of Philosophical Logic 49 (6):1091-1109.
    If one takes seriously the idea that a scientific language must be extensional, and accepts Quine’s notion of truth-value-related extensionality, and also recognizes that a scientific language must allow for singular terms that do not refer to existing objects, then there is a problem, since this combination of assumptions must be inconsistent. I will argue for a particular solution to the problem, namely, changing what is meant by the word ‘extensionality’, so that it would not be the truth-value that had (...)
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  2. State-of-affairs Semantics for Positive Free Logic.Hans-Peter Leeb - 2006 - Journal of Philosophical Logic 35 (2):183-208.
    In the following the details of a state-of-affairs semantics for positive free logic are worked out, based on the models of common inner domain - outer domain semantics. Lambert's PFL system is proven to be weakly adequate (i.e., sound and complete) with respect to that semantics by demonstrating that the concept of logical truth definable therein coincides with that one of common truth-value semantics for PFL. Furthermore, this state-of-affairs semantics resists the challenges stemming from the slingshot argument since logically equivalent (...)
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  3. Zur Deutung von Axiomensystemen bei Popper.Hans-Peter Leeb - 2002 - In Edgar Morscher (ed.), Was wir Karl R. Popper und seiner Philosophie verdanken. Zu seinem 100. Geburtstag. Sankt Augustin: Academia Verlag. pp. 133-159.
    In Popper's Logik der Forschung, a theoretical system is a set of sentences that describe a particular sub-area of science, in particular of empirical science. The goal of axiomatizing a theoretical system is to specify a small number of "axioms" describing all presuppositions of the sub-area under consideration, so that all other sentences of this system can be derived from them by means of logical or mathematical transformations. The paper discusses two philosophical interpretations of these proper axioms. First, proper axioms (...)
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  4. States of Affairs as Structured Extensions in Free Logic.Hans-Peter Leeb - forthcoming - Logic and Logical Philosophy:1.
    The search for the extensions of sentences can be guided by Frege’s “principle of compositionality of extension”, according to which the extension of a composed expression depends only on its logical form and the extensions of its parts capable of having extensions. By means of this principle, a strict criterion for the admissibility of objects as extensions of sentences can be derived: every object is admissible as the extension of a sentence that is preserved under the substitution of co-extensional expressions. (...)
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  5. A Metasemantic Analysis of Gödel's Slingshot Argument.Hans-Peter Leeb - manuscript
    Gödel’s slingshot-argument proceeds from a referential theory of definite descriptions and from the principle of compositionality for reference. It outlines a metasemantic proof of Frege’s thesis that all true sentences refer to the same object—as well as all false ones. Whereas Frege drew from this the conclusion that sentences refer to truth-values, Gödel rejected a referential theory of definite descriptions. By formalising Gödel’s argument, it is possible to reconstruct all premises that are needed for the derivation of Frege’s thesis. For (...)
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  6. Das Kompositionalitätsprinzip in seinen Anwendungen auf die "Slingshot-Argumente".Hans-Peter Leeb - 2004 - Sankt Augustin: Academia Verlag.
    According to the principle of compositionality, the meaning of a composed expression depends only on its logical form and the meaning of its descriptive sub-expressions. This dependence can be understood as the substitutivity of expressions that have the same meaning without changing the meaning of the composed expression. In this book the hidden complexity of Frege's and Quine's conceptions of extensionality is revealed. The insights gained by this analysis as well as two versions of the principle of compositionality are used (...)
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  7. Sachverhalte und Extensionalität in der freien Logik.Hans-Peter Leeb - 2006 - Sankt Augustin: Academia Verlag.
    Empty individual expressions are needed to reconstruct the actual use of scientific language as well as to make logic free from existence assumptions. According to Quine, a language must be extensional to be adequate for the purposes of science. By means of Lambert's non-extensionality argument it can be demonstrated that a language containing empty individual expressions cannot be extensional as long as truth-values are the extensions of sentences. This book investigates the soundness of Lambert's argument and examines the question of (...)
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  8. E. Morscher's Normenlogik. Grundlagen - Systeme - Anwendungen (2012). [REVIEW]Hans-Peter Leeb - 2014 - Grazer Philosophische Studien 90 (1):354-355.
    The review gives a short decription of the content of the book and several improvements and corrections of its content.
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  9. G. Priest's An Introduction to Non-Classical Logic (2001). [REVIEW]Hans-Peter Leeb - 2003 - History and Philosophy of Logic 24:65-66.
    The review gives a short description of the content of the book and discusses the treatment of conditionals in it.
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  10. Karel Lambert, Free Logics: Their Foundations, Character, and Some Applications Thereof (Prophil Projekte zur Philosophie Bd. 1. Eine Schriftenreihe des Forschungsinstituts Philosophie/Technik/Wirtschaft an der Universität Salzburg). Sankt Augustin: Academia-Verlag, 1997. 156 pp. Asch. 239. ISBN 3-89665-000-9. [REVIEW]Hans-Peter Leeb - 2001 - History and Philosophy of Logic 22:233-236.
    Free logics aim at freeing logic from existence assumptions by making them explicit, e.g., by adding an existence premisse to the antecedence of the classical axiom-schema of Universal Instantiation. Their historical development was motivated by the problem of empty singular terms, and that one of simple statements containing at least one such singular term: what is the referential status of such singular terms and what truth-value, if any, do such statemants have? Free logics can be classified with regard to their (...)
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