28.21 As we have seen, verbs are alphabetized by their 1st person, singular, present, indicative, active form, with a –μι or –ω ending. This is the FIRST PRINCIPAL PART.
The SECOND PRINCIPAL PART is the 1st person, singular, future, indicative, active. This form is necessary because adding –σ– to the verb stem can result in some unexpected results.
The THIRD PRINCIPAL PART is the 1st person, singular, aorist, indicative, active. The third principal part of a verb shows whether it forms a FIRST or SECOND AORIST, and if the latter, whether it is THEMATIC or ATHEMATIC. For example:
- βουλεύω, βουλεύσω, ἐβούλευσα (First Aorist)
- λείπω, λείψω, ἔλιπον (Second Aorist Thematic)
- βαίνω, βήσομαι, ἔβην (Second Aorist Athematic)