The first requirement of a criminal justice system is to define clearly punishable conduct, so that those to whom the law applies cannot misunderstand what is expected of them. The same standard of clarity should apply to the English prison rules by which inmates are disciplined. An analysis of these rules shows them to be frequently too general and ambiguous, such that arbitrary and unjust treatment of inmates may occur under the rules. The most objectionable rule is the one that states an inmate is guilty of an offense against discipline if he in any way 'offends against good order and discipline.' This 'drag-net' offense makes it possible for prison authorities to introduce innumerable offenses without submitting them to a formal test for inclusion among the other prison rules. This rule should be abolished. Another rule provides for an inmate to be disciplined when he 'makes any false and malicious allegation against an officer.' This has a chilling effect upon inmates' pursuit of grievances against officers. The grievance procedures should determine the truth of an inmate complaint against an officer without consequences for the inmate according to the outcome. Another rule provides for discipline where there are repeatedly groundless complaints by an inmate. Other rules critiqued bear upon mutiny, gross personal violence, escape, possession of unauthorized articles, disrespectful treatment and improper language, disobeying an order, and carelessness at work. Footnotes and 18 references are provided.