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1. Rigidity is a property of relations/properties, a meta-property. It is defined in terms of modal logic.
  • A property of an entity is essential to that entity if it must be true of it in every possible world, i.e. if it necessarily holds for that entity.
  • A property is rigid if it is essential to all its possible instances; an instance of a rigid property cannot stop being an instance of that property in a different world.


  • Rigidity as a meta-property is not “inherited” by sub-properties of properties that carry it. [ Guarino & Welty, 2003(?) ]