A Theory of Conditionals

Stalnaker's 1968 paper inaugurating the possible-worlds semantics for indicative and counterfactual conditionals

Tradition: Analytic metaphysics / possible-worlds semantics / philosophy of language

Stalnaker's 1968 founding paper of the possible-worlds semantics for conditionals — the 'Stalnaker conditional'

Published in Nicholas Rescher (ed.), 'Studies in Logical Theory' (American Philosophical Quarterly Monograph Series 2, Blackwell 1968, pp. 98-112), 'A Theory of Conditionals' inaugurates the possible-worlds semantics for indicative and counterfactual conditionals that, alongside David Lewis's subsequent 'Counterfactuals' (1973), defined the field. Stalnaker's distinctive thesis: 'if A then B' is true at a world w iff B is true at the closest A-world to w — a selection-function semantics where some unique 'nearest' A-world is selected for each world w. Stalnaker assumes uniqueness of the selected nearest world (giving rise to the Conditional Excluded Middle: 'if A then B' or 'if A then not-B'); Lewis would later argue (in 'Counterfactuals') that no unique nearest world need exist (giving rise to a more complex 'closeness ordering' semantics). The two approaches define the central technical-philosophical controversy in modern philosophy of conditionals. Stalnaker's paper also extends the framework from indicative to subjunctive conditionals — including counterfactuals about the past — and treats the philosophical-conceptual issues (what 'closeness' means, what its semantics requires) with greater explicitness than Lewis's later work. The paper has been continuously productive: it founded the modern philosophy of conditionals, made possible the modern analysis of counterfactual reasoning across the sciences, and is the principal Stalnaker contribution to the contemporary metaphysics of modality (alongside the body of work collected in 'Ways a World Might Be' (2003) and 'Context' (2014)).