In order to explain, after these antecedents, the origin of the infinitive in ειν, as τύπτειν, we must admit either the shortening of ναι to νι, which is difficult; or the existence of a locative in ι by the side of a dative in αι. That the locative can take the place of the dative we see clearly in the Sanskrit forms of the aorist, +parsháṇi+, to cross, +nesháṇi+, to lead, which, as far as their form, not their origin, is concerned, would well match Greek forms like λύσειν in the future. In either case, τύπτε-νι in Greek would have become τύπτειν, just as τύπτε-σι became τύπτεις. In the Doric dialect this throwing back of the final ι is omitted in the second person singular, where the Dorians may say ἀμέλγες for ἀμέλγεις; and in the same Doric dialect the infinitive, too, occurs in εν instead of ειν; _e.g._, ἀείδεν instead of ἀείδειν. (Buttman, “Greek Gr.,” § 103, 10, 11.) In this manner the growth of grammatical forms can be made as clear as the sequence of any historical events in the history of the world, nay, I should say far clearer, far more intelligible; and I should think that even the first learning of these grammatical forms might be somewhat seasoned and rendered more really instructive by allowing the pupil, from time to time, a glimpse into the past history of the Greek and Latin languages. In English what we call the infinitive is clearly a dative; _to speak_ shows by its very preposition what it was intended for. How easy, then, to explain to a beginner that if he translates, “able to speak,” by ἱκανὸς εἰπεῖν, the Greek infinitive is really the same as the English, and that εἰπεῖν stands for εἴπενι and this for εἴπεναι, which, to a certain extent, answers the same purpose as the Greek ἔπει, the dative of ἔπος, and therefore originally ἔπεσι.