S.I.: NEW DIRECTIONS IN THE EPISTEMOLOGY OF MODALITY
Deﬂationism about the necessary a posteriori and Twin
Received: 19 December 2017 / Accepted: 26 May 2018
© Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract Some necessary truths are a posteriori. That’s widely agreed and is pre-
sumed here. Their existence might appear to show that discoveries about how things
are in fact—about how things actually are—can lead to discoveries about all the ways
things might be, about the nature of logical space. I detail one way of resisting this
conclusion for a number of examples, and the implications of Twin Earth for the issue.
Central is the notion of a Cambridge discovery.
Keywords Necessary a posteriori · Twin Earth · Cambridge discovery · Names
1 Cambridge discoveries and deﬂationism about the necessary
How things are in one location can tell us about how things are elsewhere. Its being hot
in one place can tell us that it is hot in the places we know the weather is coming from.
Sounds heard in one place can tell us about distant explosions. The visual experiences
of a golfer on the fairway tell her about what’s happening on the green ahead. And so
on. A feature of examples like these is that we have recourse to what we know about
the connections between how things are where we are and how things are distant from
where we are. There are, however, things we can discover about how things are distant
from where we are that require no recourse to such knowledge—or so it might seem.
If we discover that where we are it is raining, we can infer that any place where it is not
raining is not where we are. We can also infer that any place where it is raining is like
where we are in at least one way. The reader will be able to construct many more exam-
Australian National University, Canberra, Australia