Counterpart Theory and Quantified Modal Logic |
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Lewis (David) |

Source: Lewis - Philosophical Papers Volume I, Part 1: Ontology, Chapter 3 |

Paper - Abstract |

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- In this landmark paper, Lewis outlines his theory of modality
^{1}and counterparts. The eight postulates constitutive of Lewis's counterpart theory are expressed in an extensional first-order language that replaces the modal^{2}operators (characteristic of traditional quantified modal logic)^{3}with four primitive predicates:

… 'x is a possible world',

… 'x is in possible world y',

… 'x is actual', and

…'x is a counterpart of y'. - Upon presenting a scheme for translating sentences expressed in quantified modal logic
^{4}into those expressed in his preferred extensional language, Lewis demonstrates that the latter is nevertheless a richer language; while every sentence of quantified modal logic^{5}may be translated into a sentence expressed in counterpart theory, the reverse is not the case. - Lewis concludes the paper by considering the implications of his view for several well-known topics (notably, Aristotelian essentialism).
- The postscript includes numerous additions and emendations (including a specification of the primitive predicate, 'x is in possible world y').

Also in "Loux (Michael), Ed. - The Possible and the Actual: Readings in the Metaphysics of Modality".

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