Published online by Cambridge University Press: 03 December 2020
We consider the modality “
$\varphi $
is true in every
$\sigma $
-centered forcing extension,” denoted
$\square \varphi $
, and its dual “
$\varphi $
is true in some
$\sigma $
-centered forcing extension,” denoted
$\lozenge \varphi $
(where
$\varphi $
is a statement in set theory), which give rise to the notion of a principle of
$\sigma $
-centered forcing. We prove that if ZFC is consistent, then the modal logic of
$\sigma $
-centered forcing, i.e., the ZFC-provable principles of
$\sigma $
-centered forcing, is exactly
$\mathsf {S4.2}$
. We also generalize this result to other related classes of forcing.