Philosophia (2018) 46:295–310
In Defence of the Actuality Principle
Received: 27 May 2017 / Revised: 26 July 2017 / Accepted: 4 August 2017 /
Published online: 12 August 2017
© Springer Science+Business Media B.V. 2017
Abstract The thin red line theory is a form of branching indeterminism. It entails
that, among the many possible developments that reality might take, one is privileged:
the actual history (or ‘thin red line’). The thin red line theory is naturally paired off
with a semantic thesis that may be called ‘the actuality principle’: a statement is true
as used at a moment if and only if it is true at that moment on the actual history.
The actuality principle has been challenged, for it would be wrong about several
counterfactual reasonings. On the one hand, the actuality principle should entail that
any statement uttered at a merely possible moment is untrue. On the other hand, the
actuality principle should be at odds with the way we use subjunctive conditionals.
This paper argues that both objections rely on an inadequate understanding of the
notion of the history of use. As for the first objection, the paper argues that to assume
the actuality principle amounts to taking the actual history as the history of use. As
a consequence, one cannot consistently take the actual history as the history of use
and, at the same time, a merely possible moment as the moment of use. As for the
second objection, the paper shows that the actuality principle is consistent with any
reasonable treatment of subjunctive conditionals.
Keywords Branching time · Thin red line · Indeterminism · Ockhamist semantics ·
Department of Philosophy, Sociology, Pedagogy, and Applied Psychology, University of Padua,