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 auditur propriam turpitudinem allegans - "No one can be heard, who invokes his own guilt." Nobody can bring a case that stems from their own illegal act.⏎
Lex specialis derogat legi generali - "A law governing a specific subject matter overrides a law which only governs general matters."⏎
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.⏎
Maleficia propositis distinguuntur - "Evil acts are distinguished from (evil) purposes" or "crimes are distinguished by evil intent." Evil acts are distinguished from evil purposes[4] crimes are distinguished by the intention[5]⏎