Originally Posted by JohnMacWW

I do not entirely agree with this (and I am both a lawyer and part-time law professor ). If a law says that you can or cannot do something, it is almost always accompanied by situations where that law is not applicable. The result is that we use the term "general rule" as a casual reference to the black letter part of a law or the rule that applies in most situations. The term "general rule" is not an exact defined term.

Most laws contain exceptions when they are enacted. Others gain exceptions through court interpretations or in "rulemaking" to adopt regulations that enforce the law. If, however, the state (police, prosecutor, etc) choose not to enforce a law either on occasion or generally, then then the law is still there, but the state choosing not to enforce it does not make that an "exception." In fact you have to be careful treating the situation as an "exception" because the state could choose to applly the law to you.

So it is the case that there is almost always a "general rule" that is the usual legal requirement and then "exceptions" which are special situations that are legally recognized. Non-enforcement, however, falls into a different category.

So, e.g. as a general rule, intentionally killing someone is usually one of several crimes usually called "Murder", "Homicid" or Manslaughter". But, if you kill someone in "self defense" you are usually not considered to have committed murder. Self defense is an exception of the general rule of homicide. If the prosecutor chooses not to prosecute someone who killed someone under some odd circumstances, that does not create a new exception and there is no guarantee that another siutation, with the same facts might not result in prosecution.