Lex retro non agit - "The law does not operate retroactively." A law cannot make something illegal that was legal at the time it was performed. See ex post facto law.⏎
Nemo debet esse iudex in propria - "No one shall be a judge in his own case." In the past it was thought that it included just two rules namely (1) nemo debet esse judex in propria causa (no one shall be a judge in his own case).⏎
Lex specialis derogat legi generali - "A law governing a specific subject matter overrides a law which only governs general matters."⏎
Nemo dat quod non habet - [6] The basic rule that a person who does not own property (e.g. a thief) cannot confer it on another except with the true owner's authority (i.e. as his agent). Exceptions to this rule include sales under statutory powers, and cases where the doctrine of estoppel prevents a legal owner from denying a seller's right to sell.⏎