When we approach the Third Period, it might seem that here, at least, there could be no difference of opinion between Professor Curtius and myself. That Third Period represents simply what I called the first setting in of _combination_, following after the _isolating_ stage. Curtius calls it the _primary verbal period_, and ascribes to it the origin of such combinatory forms as +dấ-ma+, give-I, +dâ-tva+, give-thou, +dấ-ta+, give-he; +dâ-ma-tvi+, give-we, +dâ-tva-tvi+, give-you, +dâ-(a)nti+, give-they. These verbal forms he considers as much earlier than any attempts at declension in nouns. No one who has read Curtius’ arguments in support of this chronological arrangement would deny their extreme plausibility; but there are grave difficulties which made me hesitate in adopting this hypothetical framework of linguistic chronology. I shall only mention one, which seemed to me insurmountable. We know that during what we called the First Radical Period the sway of phonetic laws was already so firmly established, that, from that period onward to the present day, we can say, with perfect certainty, which phonetic changes are possible, and which are not. It is through these phonetic laws that the most distant past in the history of the Aryan language is connected with the present. It is on them that the whole science of etymology is founded. Only because a certain root has a tenuis, a media, an aspirate, or a sibilant, is it possible to keep it distinct from other roots. If t and s could be interchanged, then the root +tar+, to cross, would not be distinct from the root +sar+, to go. If d and +dh+ could vary, then +dar+, to tear, would run together with +dhar+, to hold. These phonetic distinctions were firmly established in the radical period, and continue to be maintained, both in the undivided Aryan speech, and in the divided national dialects, such as Sanskrit, Greek, Latin, and Gothic. How then can we allow an intervening period, during which +ma-tvi+, could become +masi+, +tva-tvi+, +thas+, and the same +tva-tvi+ appear also as +sai+? Such changes, always most startling, may have been possible in earlier periods; but when phonetic order had once been established, as it was in what Curtius calls his first and second periods, to admit them as possible, would be, as far as I can judge, to admit a complete anachronism. Of two things one; either we must altogether surrender those chaotic changes which are required for identifying Sanskrit e with Greek μαι, and Greek μαι with +mâ-ma+, etc., or we must throw them back to a period anterior to the final settlement of the Aryan roots.