Remarks

1. We have mentioned various ways of getting new contexts from old ones: by specializing the time or place, by specializing the situation, by making abbreviations, by specializing the subject matter (e.g. to U.S. legal history), by making assumptions and by specializing to the context of a conversation. These are all specializations of one kind or another. Getting a new context by transcending an old context, e.g. by dropping the assumption of a gravitational field, gives rise to a whole new class of ways of getting new contexts.

   These are too many ways of getting new contexts to be treated separately.

2. We have used natural language examples in this article, although natural language is not our main concern. Nevertheless, I hope that formalizing context in the ways we propose may be useful in studying the semantics of natural language. Natural language exhibits the striking phenomenon that context may vary on a very small scale; several contexts may occur in a single sentence.

   Consider the context of an operation in which the surgeon says, ``Scalpel''. In context, this may be equivalent to the sentence, ``Please give me the number 3 scalpel''.

3. $ist(c,p)$ can be considered a modal operator dependent on $c$ applied to $p$. This was explored in [Shoham, 1991].

4. It would be useful to have a formal theory of the natural phenomenon of context, e.g. in human life, as distinct from inventing a form of context useful for AI systems using logic for representation. This is likely to be an approximate theory in the sense described in [McCarthy, 1979a]. That is, the term ``context'' will appear in useful axioms and other sentences but will not have a definition involving ``if and only if''.

5. Useful nonmonotonic rules for lifting will surely be more complex than the examples given.