Bounded forcing axioms as principles of generic absoluteness

We show that Bounded Forcing Axioms (for instance, Martin's Axiom, the Bounded Proper Forcing Axiom, or the Bounded Martin's Maximum) are equivalent to principles of generic absoluteness, that is, they assert that if a \(\Sigma_1\) sentence of the language of set theory with parameters of small transitive size is forceable, then it is true. We also show that Bounded Forcing Axioms imply a strong form of generic absoluteness for projective sentences, namely, if a \(\Sigma^1_3\) sentence with parameters is forceable, then it is true. Further, if for every real x, \(x^{\sharp}\) exists, and the second uniform indiscernible is less than \(\omega_2\), then the same holds for \(\Sigma^1_4\) sentences.

Authors and Affiliations

1. Departament de Lògica, Història i Filosofia de la Ciència, Universitat de Barcelona, Baldiri Reixac s/n, 08028 Barcelona, Spain (e-mail: bagaria@trivium.gh.ub.es) , , , , , , ES

   Joan Bagaria

Received: 20 February 1998

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