In this provocative book, Michael Tye presents his unique account of the metaphysical foundations of psychological discourse. In place of token identity theory or eliminative materialism, he advocates a generalisation of the adverbial approach to sensory experience, the 'operator theory'. He applies this to the analysis of prepositional attitudes, arguing that mental statements cannot involve reference to mental events or objects and that therefore causal statements about the mental cannot be regarded as asserting relations between events. This adverbial theory has the virtue of being both simple and systematic and is an important contribution to the philosophy of mind.