| Information about a system is not our knowledge about it. Information is our ignorance, the ignorance of something to which we may or may not have access. A mail address, as a state of a system, can be an information if we do not know it. We may say that a system contains information if we do not have complete knowledge about it and that we cannot predict its exact state at any moment. If we completely know a system as in deterministic science, it's information is zero. In all probabilistic theories of today, it has always been claimed that the information we treated was complete. If we know it, any questions which can be asked about the system of interest can be exactly answered. For detailed discussions on complete information theory, see, e.g., Claude Shannon |