I think their is a mix up, since their are three categories, (1) Alibi & Mistake of law/fact, intoxication (in NY) etc. are actually not defenses at all, they simply negate the mens rea with an external fact/law (by creating a reasonable doubt), that usu. means defense attorney has to produce evidence & persuade but the prosecutor need NOT disprove beyond a reasonable doubt (BARD). (2) True defenses NEED introduce an internal element that negates a CRIME element (e.g. self-defense, justification, defense of 3rd p. etc.), prosecutor needs to disprove these BARD, only some evidence required--just production by defense counsel. (3) Affirm. Def. require produce & persuade, (e.g. insanity, most heat of passion, diminished responsibility, duress, EXECUSES,entrapment) prosecutor usu. needs to disprove these BARD, though some states differ & each defense differs. Quick short hand: (1) element negators poke holes in State's case, (2) defenses usu. assert elements of crime present, but conduct justified--no "wrong" crime was committed, & (3) affirm def. assert this person execused cuz of some special fact/law. Hope this helps!