1. indicates passive voice (incl. the "suffering passive") (～れる connects to -nai stem of 五段 verbs and to サ変 as さ～れる; ～られる connects to -nai stem of 一段 and カ変 verbs and to サ変 as せ～られる)

2. indicates the potential form (no imperative form, not used on 五段 in modern speech)

3. indicates spontaneous occurrence (no imperative form)

4. used as an honorific for others' actions (Honorific, no imperative form)