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First page of Proofs Without Nominals: Gödel's Ontological Argument, its Shallow Embedding, and the Open Questions of the Monatshefte Notes

Proofs Without Nominals: Gödel's Ontological Argument, its Shallow Embedding, and the Open Questions of the Monatshefte Notes

Christoph Benzmüller

cs.LO Sep 28, 2026 · v1 cs.AI math.LO
All theorems about Gödel's ontological argument variants are verified independently in Lean 4 alongside Isabelle/HOL, via a Lean port of the developments.
The shallow embedding of higher-order modal logic in classical higher-order logic, used in Benzmüller and Scott's Notes on Gödel's and Scott's variants of the ontological argument (2025), reaches beyond the modal object language of the arguments: its property quantifiers range over terms that may also express nominals and satisfaction operators of hybrid logic, and a proof using one proves a theorem of the embedding that need not be one of the modal logic. That the framework affords this is not new, and whether a result is one of the modal logic can be settled in two ways: by replaying it in an explicit proof calculus, done by hand for chosen theorems, or by analysing the proofs the embedding itself produces, which this article does mechanically, for every result at once. Every statement the Notes prove has a proof inside the object language: 294 written out by hand and machine-checked, none using a nominal. The proofs the Notes themselves give instantiate no nominal either; what the detector flags there are terms a prover substituted. The three questions the Notes leave open are settled too, and without nominals, but the conjunction axiom has to be emended: generalised in the Notes to Gödel's "any number of summands", it covers the conjunction of no properties, and of one; the empty one alone settles all three, and the two together yield what a separate axiom of Gödel's is for. This article restricts the conjunction axiom to at least two different conjuncts, the reading Gödel's footnote suggests, and the questions are settled again, by proofs that turn on the argument rather than a degenerate instance. The restriction holds of the object language only: with a nominal the axioms make the accessibility relation the identity and the readings coincide. Every theorem is verified in Isabelle/HOL and independently in Lean 4; the countermodels are Nitpick's, certified by the build.

The shallow embedding of higher-order modal logic in HOL, used in Benzmüller and Scott's Notes on Gödel's and Scott's ontological arguments, lets property quantifiers range over hybrid-logic terms such as nominals. A proof using them may establish a theorem of the embedding that is not a theorem of the modal logic. The Notes also leave three questions open.

A proof is defined as hybrid-free if every term it substitutes for a property or proposition variable belongs to the modal object language. A detector mechanically audits the recorded Isabelle proof objects of the Notes for such substitutions. Hand-written object-language proofs are machine-checked in Isabelle/HOL and in a Lean 4 port. The generalised conjunction axiom is emended to require at least two distinct conjuncts, and the open questions are re-examined under this reading.

All statements of the Notes have hybrid-free proofs: 294 written by hand and machine-checked, none using a nominal. Of 427 Isabelle facts, 403 are certified directly; the other 24 are flagged only for prover-introduced terms such as Skolem functions and library constants, and each has a certified hand-written proof. The three open questions are settled without nominals, both under the original conjunction axiom (via its empty instance) and under the emended two-conjunct version. Countermodels come from Nitpick.

Ax1GenAx1GenBoxAx1GenOneAx1GenTwo
(i) Lholdsholdsholdsholds
(ii)failsfailsholdsholds
Th4, variant 2derivablederivablederivablederivable
Th4, variant 3derivablederivablederivablerefuted
Requirements and consequences under readings of the conjunction axiom (excerpt)