41.11 An archaic imperative ending for the 2nd person singular active was –θι, which by the Classical period survived in only a few instances (S 466a):
- στῆθι (aorist from ἵστημι)
- Stand!
- φάθι or φαθί (present from φημί)
- Speak!
- γνῶθι σεαυτόν (aorist from γιγνώσκω)
- Know thyself!
- ἴθι (present form εἶμι, go)
- Go!
- ἴσθι (present from εἰμί and perfect from οἶδα)
- Be…! or Know!
41.12 The rare aorist passive/intransitive imperative uses –θι.
- λυ + θη + θι = λύθητι. (from λύω)
- Be free!
Remember that as a general rule of pronunciation in Greek, two consecutive syllables cannot each have aspiration (S 125b, G 47b). So in this case, –θη– keeps the aspiration and the imperative ending loses the aspiration: –θι → –τι.