Actions which are permitted Initially [lechatchilah] vs. Actions which are permitted only Ex Post Facto [bedieved]
Doing something which is allowed only ex post facto, initially: Yevamot 103b
Deliberately creating a situation that will require a solution that is acceptable only Bedieved: Beitzah 7b, 8a-b
The way a Mishnah presents a verb teaches us whether the Mishnah is supporting the action LeChatchilah [something permitted] or only explaining what to do Bedieved [ex post facto]: Shabbat 147a; Beitzah 7b, 8a-b; Rosh Hashanah 32b; Sotah 2b
