Do irregular Greek verbs which have two different stems in the present and aorist (like βλέπω / είδα or τρώω / έφαγα, etc.) come from a merger of two separate verbs, like go/went in English?

Answer 1

Yes. The linguistic term for this is "suppletion". In our paradigm of the verb "to be" three different verbs have been combined: one giving "be, been", another for "is, are" and a third for "was, were". Suppletion is a fairly

common phenomenon.