Misplaced Pages

Neighborhood semantics

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.

Neighborhood semantics, also known as Scott–Montague semantics, is a formal semantics for modal logics. It is a generalization, developed independently by Dana Scott and Richard Montague, of the more widely known relational semantics for modal logic. Whereas a relational frame ⟨ W , R ⟩ {\displaystyle \langle W,R\rangle } consists of a set W of worlds (or states) and an accessibility relation R intended to indicate which worlds are alternatives to (or, accessible from) others, a neighborhood frame ⟨ W , N ⟩ {\displaystyle \langle W,N\rangle } still has a set W of worlds, but has instead of an accessibility relation a neighborhood function

N : W → 2 2 W {\displaystyle N:W\to 2^{2^{W}}}

that assigns to each element of W a set of subsets of W. Intuitively, each family of subsets assigned to a world are the propositions necessary at that world, where 'proposition' is defined as a subset of W (i.e. the set of worlds at which the proposition is true). Specifically, if M is a model on the frame, then

M , w ⊨ ◻ φ ⟺ ( φ ) M ∈ N ( w ) , {\displaystyle M,w\models \square \varphi \Longleftrightarrow (\varphi )^{M}\in N(w),}

where

( φ ) M = { u ∈ W ∣ M , u ⊨ φ } {\displaystyle (\varphi )^{M}=\{u\in W\mid M,u\models \varphi \}}

is the truth set of φ {\displaystyle \varphi } .

Neighborhood semantics is used for the classical modal logics that are strictly weaker than the normal modal logic K.

Correspondence between relational and neighborhood models

To every relational model M = (W, R, V) there corresponds an equivalent (in the sense of having pointwise-identical modal theories) neighborhood model M' = (W, N, V) defined by

N ( w ) = { ( φ ) M ∣ M , w ⊨ ◻ φ } . {\displaystyle N(w)=\{(\varphi )^{M}\mid M,w\models \Box \varphi \}.}

The fact that the converse fails gives a precise sense to the remark that neighborhood models are a generalization of relational ones. Another (perhaps more natural) generalization of relational structures are general frames.

References

  • Chellas, B.F. Modal Logic. Cambridge University Press, 1980.
  • Montague, R. "Universal Grammar", Theoria 36, 373–98, 1970.
  • Scott, D. "Advice on modal logic", in Philosophical Problems in Logic, ed. Karel Lambert. Reidel, 1970.


Stub icon

This logic-related article is a stub. You can help Misplaced Pages by expanding it.

Categories: