  RS-frames were introduced by Gehrke as relational semantics for substructural
logics. They are two-sorted structures, based on RS-polarities with additional
relations used to interpret modalities. We propose an intuitive, epistemic
interpretation of RS-frames for modal logic, in terms of categorization systems
and agents' subjective interpretations of these systems. Categorization systems
are a key to any decision-making process and are widely studied in the social
and management sciences.
  A set of objects together with a set of properties and an incidence relation
connecting objects with their properties forms a polarity which can be `pruned'
into an RS-polarity. Potential categories emerge as the Galois-stable sets of
this polarity, just like the concepts of Formal Concept Analysis. An agent's
beliefs about objects and their properties (which might be partial) is modelled
by a relation which gives rise to a normal modal operator expressing the
agent's beliefs about category membership. Fixed-points of the iterations of
the belief modalities of all agents are used to model categories constructed
through social interaction.
