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2017 | OriginalPaper | Buchkapitel

Automating Emendations of the Ontological Argument in Intensional Higher-Order Modal Logic

verfasst von : David Fuenmayor, Christoph Benzmüller

Erschienen in: KI 2017: Advances in Artificial Intelligence

Verlag: Springer International Publishing

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Abstract

A shallow semantic embedding of an intensional higher-order modal logic (IHOML) in Isabelle/HOL is presented. IHOML draws on Montague/Gallin intensional logics and has been introduced by Melvin Fitting in his textbook Types, Tableaus and Gödel’s God in order to discuss his emendation of Gödel’s ontological argument for the existence of God. Utilizing IHOML, the most interesting parts of Fitting’s textbook are formalized, automated and verified in the Isabelle/HOL proof assistant. A particular focus thereby is on three variants of the ontological argument which avoid the modal collapse, which is a strongly criticized side-effect in Gödel’s resp. Scott’s original work.

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Fußnoten
1
In this paper we work with the Isabelle/HOL proof assistant [22], which explains the chosen abbreviation. Generally, however, the work presented here can be mapped to any other system implementing Church’s simple type theory [13].
 
2
This term was originally coined by Fitelson and Zalta in [14] and describes an emerging, interdisciplinary field aiming at the rigorous formalization and deep logical assessment of philosophical arguments in an automated reasoning environment.
 
3
More loosely related work studied Anselm’s older, non-modal version of the ontological argument directly in Prover9 [23] and PVS [24].
 
4
In contrast to deep semantic embeddings, where the embedded logic is presented as an abstract datatype, our shallow semantic embeddings avoid inductive definitions and maximize the reuse of logical operations from the meta-level. In particular, tedious new binding mechanisms are avoided in our approach.
 
5
Possibilist and actualist quantification can be seen as the semantic counterparts of the concepts of possibilism and actualism in the metaphysics of modality. They relate to natural-language expressions such as ‘there is’, ‘exists’, ‘is actual’, etc.
 
6
The notion of rigid designation was introduced by Kripke in [21], where he discusses its many interesting ramifications in logic and the philosophy of language.
 
7
We prove theorems in Isabelle by using the keyword ‘by’ followed by the name of a proof method. Some methods used here are: simp (term rewriting), blast (tableaus), meson (model elimination), metis (ordered resolution and paramodulation), auto (classical reasoning and term rewriting) and force (exhaustive search trying different tools). In our computer-formalization and assessment of Fitting’s textbook [17], we provide further evidence that our embedded logic works as intended by verifying the book’s theorems and examples.
 
8
We utilize here (counter-)model finder Nitpick [12] for the first time. For the conjectured lemma, Nitpick finds a countermodel (not shown here), i.e. a model satisfying all the axioms which falsifies the given formula.
 
9
The de dicto/de re distinction is used regularly in the philosophy of language for disambiguation of sentences involving intensional contexts.
 
10
Implication can also be proven in the reverse direction (which is not needed for our purposes). Using these definitions, we can derive axioms for the most common modal logics (see also [5]). Thereby we are free to use either the semantic constraints or the related Sahlqvist axioms. Here we provide both versions. In what follows we use the semantic constraints for improved performance.
 
11
To prove T1, the fact is used that positive properties cannot entail negative ones (A2), from which the possible instantiation of positive properties follows. A computer-formalization of Leibniz’s theory of concepts can be found in [1], where the notion of concept containment in contrast to ordinary property entailment is discussed.
 
12
We provide a proof in Isabelle/Isar, a language specifically tailored for writing proofs that are both computer- and human-readable. We refer the reader to [17] for other proofs not shown in this article.
 
13
Essence is defined here (and in Fitting’s variant) in the version of Scott; Gödel’s original version leads to the inconsistency reported in [9, 10].
 
14
In what follows, the ‘ https://static-content.springer.com/image/chp%3A10.1007%2F978-3-319-67190-1_9/450601_1_En_9_IEq29_HTML.gif ’ parentheses are used to convert an extensional object into its ‘rigid’ intensional counterpart (e.g. https://static-content.springer.com/image/chp%3A10.1007%2F978-3-319-67190-1_9/450601_1_En_9_IEq30_HTML.gif ).
 
15
Fitting’s original treatment in [15] left several details unspecified and we had to fill in the gaps by choosing appropriate formalization variants (see [17] for details).
 
16
Gödel’s original axioms (without Scott’s addition) are proven inconsistent in [9].
 
17
This theorem’s proof could be completely automatized for Gödel’s and Fitting’s variants. For Anderson’s version however, we had to reproduce in Isabelle/HOL the original natural-language proof given by Anderson (see [3], Theorem 2*, p. 296).
 
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Metadaten
Titel
Automating Emendations of the Ontological Argument in Intensional Higher-Order Modal Logic
verfasst von
David Fuenmayor
Christoph Benzmüller
Copyright-Jahr
2017
DOI
https://doi.org/10.1007/978-3-319-67190-1_9

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