 The error of confusing the Church-Turing thesis properly so called with one or another form of the maximality thesis has led to some remarkable claims in the foundations of psychology. For example, one frequently encounters the view that psychology must be capable of being expressed ultimately in terms of the Turing machine (e.g., Fodor 1981: 130; Boden 1988: 259). To one who makes this error, conceptual space will seem to contain no room for mechanical models of the mind that are not equivalent to Turing machines. Yet it is certainly possible that psychology will find the need to employ models of human cognition transcending Turing machines.