Nemo judex in sua causa - "No one shall be a judge in his own case." Prevents conflict of interest in courts. Often invoked when there is really no conflict, but when there is even the appearance of one.⏎
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.⏎
Jura novit curia - "The court knows the law." Concept that parties to a case do not need to define how the law applies to their case. The court is solely responsible for determining what laws apply.⏎