 According to externalists, when A is processing S and B is processing S′, they are in computational states of different types. According to internalists, A and B are in computational states of the same type. In other words, externalists maintain that computational states are individuated in part by their reference, which is determined at least in part by physical properties external to the system. By contrast, internalists maintain that computational states are individuated in a way that depends solely on the intrinsic physical properties of cognitive systems.