Modality is important for logical AI. An agent must reason about what it or other agents know, believe, want, intend or owe [him] a choice. Referentially opaque modalities are needed and must be formalized correctly. Modal logics are sometimes decideable---an important virtue. Unfortunately, modal logics seem too limited for many important purposes. This article contains examples of uses of modality for which modal logic seems inadequate.

I have no proof that modal logic is inadequate, so I hope modal logicians will take the examples as challenges.

There are .html, .dvi, .pdf and .ps versions.

The paper will appear in a special issue of Studia Logica devoted to the combination of logics.

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