:Dear Damorbel, you have a serious problem of understanding: you are more or less insensitive to overall or large-scale inferential structure in physics. Overall inferential structure is important in the presentation of physics. In times past, inferential structure was taught as part of the syllabus in dialectic and logic, but it seems that you did not attend to it, and have not developed a sensitivity to it through experience in study of physics. Important distinctions that are made in logic and dialectic are between definitions, theoretical principles, axioms or postulates, empirical observations and demonstrations, empirical generalizations, inferences, deductions, inductions, abductions, hypotheses, assertions, assumptions, conclusions, contradictions, inconsistencies, incoherences, and theorems. These all have their places in the presentation of physics, but you seem more or less unable to see how they fit together to provide overall inferential structure, apparently because you have not attended to it or do not value it. Your rhetorical questions just above seem to support this reading of the appearances. As I have mentioned before, you may not be entirely to blame for your difficulty here: some writers, including Kittel & Kroemer, and Reif, regrettably think they are very clever in trying to teach thermodynamics as a consequence of or as part of statistical mechanics. Thus Kittle & Kroemer actually entitle their text Thermal Physics; the result is that students become muddled about the overall inferential structure of the subjects, and get into the difficulties such as those that beset you. Until you understand and try to remedy this problem, you will continue to be more or less beyond help.