 The view that programs are theories goes back to approaches in cognitive science. In the context of the so-called Information Processing Psychology (IPP) for the simulative investigation on human cognitive processes, Newell and Simon (1972) advanced the thesis that simulative programs are empirical theories of their simulated systems. Newell and Simon assigned to a computer program the role of theory of the simulated system as well as of the simulative system, namely the machine running the program, to formulate predictions on the simulated system. In particular, the execution traces of the simulative program, given a specific problem to solve, are used to predict the mental operation strategies that will be performed by the human subject when asked to accomplish the same task. In case of a mismatch between execution traces and the verbal reports of the operation strategies of the human subject, the empirical theory provided by the simulative program is revised. The predictive use of such a computer program is comparable, according to Newell and Simon, to the predictive use of the evolution laws of a system that are expressed by differential or difference equations.