§ ΐ2δ] Ablaut (Vowel Gradation) 49 § 125. The ablaut-series as given in § 124 have, for practical reasons, been limited to the phases of ablaut as they appear in the various classes of strong verbs. From an Indo-Germanic point of view the series I-V belong to one and the same series which underwent in Germanic various modifications upon clearly defined lines. What is called the sixth ablaut-series in the Germanic languages is really a mixture of several original series, owing to several Indg. vowel-sounds having fallen together in prim. Germanic ; thus the a, which occurs in the present and the past participle, corresponds to three Indg. vowels, viz. a (§ 36), ο (§ 39), and a (§ 41); and the ō in the preterite corresponds to Indg. a (§42) and Indg. ō (§ 45). In a few isolated cases there are also phases of ablaut which do not manifest themselves in the various parts of strong verbs, as e. g. ace. pi. *aúhsa-ns, oxen: gen. pi. aúhs-nē, where the vowel disappears altogether, as in Gr. πέτομ,αι: e-πτ-ό/ι,ημ; slauhts, slaughter: slahan (VI), to slay; lats, slothful: lētan(VII), to let; raþjō, number, account: redan (VII), to counsel; lūkan, to lock: pret. sing, láuk (II), which is an aorist-present like Gr. τύψω, τρίβω, another similar aorist-present form is truđan (IV), to tread. For the phases of ablaut which do not occur in the various parts of strong verbs, and for traces of ablaut-series other than those given above, the student should consult Brugmann's Kurze vergleichende Grammatik der indogermanisc':cn Spraclien, pp. 138-50.
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