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L ogic A crucial notion for central-state materialism or the identity theory . This theory in the philosophy of mind claims that mental states or processes are nothing other than processes in the brain. But linguistics argued that the logic of statements about brain states and the logic of statements about mental states are different and that brains and minds cannot therefore be identical. To deal with this objection, physicalism introduced the notion of contingent identity to say that the identity between mental states and brain states is not logical or necessary identity. Expressions for the states are not identical in meaning, but pick out the same items contingently or accidentally, and the identity holds as a matter of contingent fact. The identity is not a conceptual truth. The world could have been otherwise, but it happens to be the case that mental states are brain states. The notion of contingent identity has been attacked by Kripke , who claims that contingent statements involving descriptions do not reflect any genuine identity. Identity statements must be made using names rather than descriptions , but then, following Leibniz 's law , if an identity statement is true, it must be necessarily true. “Everyone agrees that descriptions can be used to make contingent statements … Certainly when you make an identity statement using description – when you say ‘the ... log in or subscribe to read full text