Because the relation is reflexive, we will have that for any regardless of which valuation function is used. For this reason, modal logicians sometimes talk about frames, which are the portion of a relational model excluding the valuation function.

* A relational frame is a pair where is a set of possible worlds, is a binary relation on .

The different systems of modal logic are defined using frame conditions. A frame is called:

* reflexive if w R w, for every w

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