I've begun going through the pages in Smyth pertaining to the origin of personal ending,
particularly in the 2nd and 3rd singular of the present indicative (and by analogy in the lengthened subjunctive).
It seems that both of these persons have obscure origin in non -μι verbs.
From Hom. ἐσσι (2nd.s. of εἰμί), Smyth shows a probable origin of 2nd person
in λῡ-ε-σι » λῡε-ϊ » λῡει to which ς was added (why was it added and when?)
But the 3rd person, he notes, cannot be derived from λῡ-ε-σι for λῡ-ε-τι, the 3rd.s
ending of -μι verbs.
So I was wondering if any scholar has since been able to trace the exact origin of the 2nd & 3rd person.