Multiple realizability, in the philosophy of mind, is the thesis that the same mental property, state, or event can be implemented by different physical properties, states or events. The idea is widely believed to have its roots in the late 1960s and early 1970s when a number of philosophers, most prominently Hilary Putnam and Jerry Fodor, put it forth as an argument against reductionist accounts of the relation between mental and physical kinds. In short, a theory of mind that includes multiple realizability allows for the existence of strong AI. The original targets of these arguments were the type-identity theory and eliminative materialism. The same arguments from multiple realizability were also used to defend many versions of functionalism, especially Machine state functionalism.