 Aristotle, General Topics: metaphysics |  Descartes, René: modal metaphysics |  identity: of indiscernibles |  identity: transworld |  Leibniz, Gottfried Wilhelm: modal metaphysics |  logic: modal |  logical truth |  material constitution |  modality: epistemology of |  natural kinds |  possible objects |  possible worlds |  Sorites paradox |  substance 