Dissertation, Birkbeck College (
2015)
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Abstract
This thesis is an argument for the view that there are problems for Modal
Reductionism, the thesis that modality can satisfactorily be defined in non-modal
terms.
I proceed via a case study of David Lewis’s theory of concrete possible worlds. This
theory is commonly regarded as the best and most influential candidate reductive
theory of modality. Based on a detailed examination of its ontology, analysis and
justification, I conclude that it does badly with respect to the following four minimal
conditions on a satisfactory reductive theory of modality: that it be (a) genuinely
reductive, (b) materially adequate, (c) conceptually adequate and (d) that its
justification provides good reason to think it true.
These problems for Lewis’s theory are not, I suggest, due to his idiosyncratic
conception of possible worlds as concrete entities. Rather, because Lewis’s theory
can be seen to represent an important class of structurally similar reductive theories
of modality, the problems for Lewis’s theory generalise to problems for these other
theories. This suggests that Modal Reductionism is unpromising. In the light of this,
the alternative approach to understanding modality, Modal Primitivism, appears
more attractive.