The familiar distinction in computer science between the actual engineering and circuitry making up a computer, and the program or set of instructions it then performs. The distinction is frequently employed in the philosophy of mind, where it may be illuminating to think of the psychological description of persons as analogous to a software description, describing the ‘program’ they are following, without reference to the particular neurophysiological set-up that enables them to function: the hardware, or more jocularly, wetware. The distinction becomes more problematic when a machine’s hardware becomes permanently modified in order to run some particular set of commands, as is the case with certain connectionist systems. See also functionalism.