Metaphysics by possible cases
We often do metaphysics by intuitions about possible cases. An example is the argument for functionalism about belief and desire. The argument starts from the premise that, intuitively, it is not possible for belief and desire to vary independently of functional nature (spelt out in some suitable way) - functional duplicates are necessarily belief-d�sire duplicates - and concludes that belief and desire are functional states. An equally famous example is the argument against functionalism for sensory qualities. The argu ment starts from the premise that, intuitively, it is possible for sensory nature to vary independently of functional nature - func tional duplicates might be sensory inverts, for example - and concludes that sensory states are not functional states.