The notion of state is ubiquitous in analysis of computational systems. State introduces intensional content into a dynamical process which cannot be directly observed from outside. Without a state, the process is defined purely by its inputoutput behaviour, and is thus expected to run itself out toward a final result, ie, compute some function. The injunction of internal data that has causal effect on the execution of a system can thus be said to be the step that extends the concept of a function to that of a process, which is no longer guaranteed to terminate.