Software is a world of myriad experiences. The computer revolution will affect philosophy most profoundly by providing a powerful new set of models and metaphors for thinking about thinking. Can thinking be reproduced by hardware running software? Is our brain hardware? Are neural patterns software? Can the interaction of pattern and patterned substance create thought? Can thought and intelligence derive from the complex interactions of unthinking and unintelligent parts?
If the answer to any of these questions is yes, then one will naturally want to know the logic of the necessary, complex interactions. But that is a distinct inquiry not to be expected here —an inquiry not into the question "what is software?" but into the question "which software makes us intelligent?"
Even if these models and metaphors were not alluring, philosophers might well pay close attention to the distinction between hardware and software, for it raises an exceptionally difficult, far-reaching, and important set of problems.
At first there appears to be little problem with the concepts of hardware and software. Hardware is the tangible machine and software is the set of instructions that makes the machine operate in specific ways. But difficulties quickly set in. Does the distinction apply to computers only or to any machine? Or will we call anything a computer if it seems to take instructions? For example, is knob-turning the software of a clock? Are tracks and their switches the software of trains? Is Bach's written score to the Art of the Fugue, perhaps with a human interpreter thrown in, the software of an organ?
In any case, what are "instructions" to a machine? If they are merely thought, or written in English with pencil on paper, they will not (yet) direct the behavior of machines. But if they are given a material form —such as punched cards or magnetic tape— and enter the causal web of the machine's physical operation, why do we not call them hardware?
The question of this essay is unabashedly metaphysical. It may be that metaphysics cannot be done, or can only be done badly. In a short essay, certainty cannot be expected on the basic notions. (See Section 13.) If this incompleteness characterizes all inquiries, it is not always admitted; and if it does not characterize all inquiries, I am not prepared to remedy it here. This essay in metaphysics is therefore modest.