2 mishnayot! 1 - If someone swears that something is factually incorrect is in fact true, or if someone swears about something that is impossible to have seen. But what if he's swearing to something as he understands it? There's concern about the plain meaning of words as people understand them. 2 - Oaths that one takes to confirm that one's statement is true - shevuat bitui - in contrast to the one taken in court. Plus, one who says "Amen" to a formulation of an oath without uttering all the words of the oath is akin to one who did utter all of the words. It amounts to taking an oath.