Is the ontological proof for God’s existence an ontological proof for God’s existence?

Marcin Tkaczyk



Two questions concerning Anselm of Canterbury’s theistic argument provided in Proslogion Ch. 2 are asked and answered: is the argument valid? under what conditions could it be sound? In order to answer the questions the argument is formalized as a first-order theory called AP2. The argument turns out to be valid, although it contains a hidden premise. The argument is also claimed not to be ontological one, but rather an a posteriori argument. One of the premises is found to be false, so the argument is claimed not to be sound and to fail to prove its conclusion.


Ratio Anselmi; ontological argument; theistic argument

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Anselmus Cantuariensis, Proslogion, in: Sancti Anselmi Cantuariensis archiepiscopi Opera omnia, vol. 1, ed. O.F.S. Schmitt, Seccovii 1938, p. 93–122 (when quoting Anselm, we provide the number of the page, however all quotations of Anselm in the present paper come from Proslogion, chapter 2 or 3).

Thomas Aquinas, Summa theologica, Textum Leonianum, Romae 1888 (we quote Aquinas traditionally, providing the number of the liber, the questio and the articulus instead of the page).

Tkaczyk, M., “Próba formalizacji wnioskowania zawartego w II rozdziale Proslogionu Anzelma z Canterbury” (“A Formalization of the argument presented in Proslogion Ch. II by Anselm of Canterbury”), Ruch Filozoficzny 58 (2006), vol. 2, 237–247.

Tkaczyk, M., Rev.: K. Świrydowicz, Podstawy Logiki modalnej. In: Roczniki Filozoficzne 54 (2006), vol. 1, 283–287.

ISSN: 1425-3305 (print version)

ISSN: 2300-9802 (electronic version)

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