Modalities: Philosophical Essays

Modalities: Philosophical Essays

Modalities: Philosophical Essays

Modalities: Philosophical Essays


Based on her earlier ground-breaking axiomatization of quantified modal logic, the papers collected here by the distinguished philosopher Ruth Barcan Marcus cover much ground in the development of her thought, spanning from 1961 to 1990. The first essay here introduces themes initially viewed as iconoclastic, such as the necessity of identity, the directly referential role of proper names as "tags", the Barcan Formula about the interplay of possibility and existence, and alternative interpretations of quantification. Marcus also addresses the putative puzzles about substitutivity and about essentialism. The collection also includes influential essays on moral conflict, on belief and rationality, and on some historical figures. Many of her views have been incorporated into current theories, while others remain part of a continuing debate.


The papers included here were written as freestanding essays. Central themes of each often rely on previous work, and there is consequently too much repetition. The alternative was radical editing, which would have made the volume questionable as a collection of previously published essays.

The essays are presented chronologically, beginning with Modalities and Intensional Languages (1961-1962). Several themes introduced there thread their way through many of the papers concerned with logical, semantical, metaphysical, and epistemological issues in intensional logic and, in particular, modalities. They concern the following:

Extensionality. Extensionality is not taken as a single principle. It is defined as characterizing a language or a theory, where a language or a theory is regarded as extensional relative to the extent to which stronger equivalence relations are equated with weaker ones. This may be done explicitly, as, for example, where property identity is reduced to set identity, or implicitly by restricting permissible predicates or contexts in such a way as to achieve a reduction that supports intersubstitutivity.

The necessity of identity. The formal proof of the necessity of identity for systems of second-order quantified modal logic is in one of several technical papers published in 1946-1947 in the Journal of Symbolic Logic. It should be noted that the proof does not depend on any peculiarly modal postulates. The necessity of identity is represented in various philosophical contexts in several subsequent papers here included. In particular, in my papers on classes, attributes, and collections (one of which, titled Classes, Collections, Assortments, and Individuals, is included here) necessary identity for collections is a derivative extension of necessary identity for individuals.

Proper names as directly referential tags. A sharp semantical distinction is drawn between names and descriptions. As in the initial essay, "a proper name [of a thing] has no meaning. It is not strongly equatable with any of the singular descriptions of the thing. . . ." Proper names are not assimilated to what later came to be called "rigid . . .

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