Weak compactness cardinals for strong logics and subtlety properties of the class of ordinals

TL;DR

This paper characterizes weak compactness cardinals for abstract logics using combinatorial properties of ordinals and explores their implications for large cardinal axioms and inner models.

Contribution

It provides a combinatorial characterization of weak compactness cardinals for all abstract logics and analyzes their relation to large cardinals like subtle and inaccessible cardinals.

Findings

Weak compactness cardinals do not imply strongly inaccessible cardinals.

Existence of a proper class of subtle cardinals is consistent with ZFC.

Weak compactness for all abstract logics implies many ordinals are strongly inaccessible in HOD.

Abstract

Motivated by recent work of Boney, Dimopoulos, Gitman and Magidor, we characterize the existence of weak compactness cardinals for all abstract logics through combinatorial properties of the class of ordinals. This analysis is then used to show that, in contrast to the existence of strong compactness cardinals, the existence of weak compactness cardinals for abstract logics does not imply the existence of a strongly inaccessible cardinal. More precisely, it is proven that the existence of a proper class of subtle cardinals is consistent with the axioms of ZFC if and only if it is not possible to derive the existence of strongly inaccessible cardinals from the existence of weak compactness cardinals for all abstract logics. Complementing this result, it is shown that the existence of weak compactness cardinals for all abstract logics implies that unboundedly many ordinals are strongly inaccessible in the inner model HOD of all hereditarily ordinal definable sets.