The appeal to necessity in restricting prisoners rights involves two distinct arguments. One argument is entirely conceptual in nature, while the other depends on empirical necessities. The conceptual argument holds that some restrictions on a prisoner's freedom of action, beyond those that hold for nonprisoners, are entailed or strictly necessitated by the very notion of imprisonment. This would include all restrictions required as the least intrusive means of enforcing the prisoner's residence in prison. This argument does little to justify the massive legal differences ordinarily found between prisoners and nonprisoners. At best, the argument can lead to the conclusion that if persons are justifiably imprisoned, their movements from place to place will justifiably be restricted to a minimal extent. Anything more than minimal restriction goes beyond what is required by the notion of imprisonment. The empirical argument is considerably more powerful than the conceptual version. It holds that the best of social systems will require certain restrictions on individual freedom to provide the greatest possible equal freedom and security for all, so that many of the restrictions that obtain in prison will be analogous to restrictions outside of prison. Whether there are exigencies in the prison system which require special restrictions of this sort, i.e., those which have no analogy to outside restrictions, is a matter for analysis. The empirical argument contains three types of premises. One details the psychological, sociological, economic, and other scientific laws which are relevent to the prison setting. Another sets out the specific circumstances which distinguish the prison settig from normal society, and the third expresses the values affected or endangered by the prison conditions. It is only when all three groups of premises are included that a conclusion can be reached about the justifiability of restricting specific rights. All three sets of premises raise difficult issues of application, with the major overall problems being the discovery, clarification, and comparison of the various values implicitly or explicitly contained in the original formulation of the argument. If these difficulties are overcome, the theoretical structure of the argument is capable of yielding rational position on whether a given right ought to be restricted. Whether the position can be applied in practice is problematical, however. Thirteen footnotes are included.