 It's easy to see, therefore, why Turing machines provided a fruitful model for early functionalist theories. However, because machine table states are total states of a system, the early functionalist equation of mental states with machine table states faded in importance as a model for the functional characterization of the complex of distinct internal states that can be simultaneously realized in a human (or other) subject (Block and Fodor 1972; Putnam 1973). Nonetheless, the idea that internal states can be fully described in terms of their relations to input, output, and one another, and can figure in lawlike descriptions, and predictions, of a system's output, was a rich and important idea that is retained by contemporary functionalist theories. And many functionalists (e.g. Rey 1997) argue that mental states are best regarded as computational states (but see Piccinini 2004 for dissent and the entry  The Computational Theory of Mind  for a comprehensive discussion of this question). 