21. The presents formed by reduplication, and by the suffixes -νη and -νυ, are nearly always transitive or "causative" in meaning, as ἵστη-μι, σκίδ-νη-μι, ὄρ-νυ-μι: whereas the simpler verbs, whether present or aorist, are usually intransitive as ἔστη-ν, ἔσβη.
Regarding the tense meaning, it is enough to point out here that the difference of the present and aorist is not given by the form of the tense: thus the imperfect ἔ-φη-ν is the same in formation as the aorist ἔ-βη-ν, ἔ-στη-ν.