- b. Before s, m should disappear, but no certain Celtic cases seem to occur. In the historic language, m before s results in mp or p as usually pronounced, as in rompa for rom + so, that is, *rom-sho; so iompaidh, umpa.
- c. Before the explosives. Original mb is now m, as in the prefix im‑, iom‑, in imleag, tom. I. E. m before t and k (q) became n (as in ceud, breug), and disappeared with compensatory lengthening. Compare also dìdean, eiridinn. Prehistoric mg, md fail us; in the present language both appear aspirated (mhgh, mhdh).
After s, m becomes in the older language mm, now m; druim comes from *dros-men. But s is very usual as an intermediate letter between a previous consonant and m: many roots appear with an additional s, which may originally have belonged to an ‑es neuter stem. We actually see such a development in a word like snaim, which in E. Ir. appears as snaidm (d. snaidmaimm), from a Celtic *snades-men. In any case, a word like ruaim postulates a Pre-Celtic *roud-s-men. See also gruaim, seaman, reim, lom, trom.
After the explosives the m is aspirated and the explosive disappears, as in the case of freumh (vṛdmâ); but seemingly the accented prefix ad- preserves the m: cf. amas, amail, aimsir.
Preserved G. m, intervocalic or final, may arise from (1) m or n before m, (2) s before m (also ‑bsm, ‑tsm, ‑dsm, ‑csm, ‑gsm), (3) ‑ngm, or ‑ṇgm, as in ceum, leum, beum, geum, or ‑ndm as in teum, (4) nꬶ becoming mb as in ìm, tum, tom, etc., or (5) mb (‑mbh), as in im‑, iom‑.
§ 5. Vowel Gradation or Ablaut.
The most characteristic roots of the I. E. languages are at least triple-barrelled, so to speak: they show three grades of vowels. The root pet, for instance, in Greek appears as pet, pot, pt (πέτομαι, fly, ποτάομαι, flutter, πτερόν, wing). The first grade—e—may be called the “normal” grade, the second the “deflected” grade, and the last—pt—the “reduced” or “weak” grade. The reason for the reduced grade is evident; the chief accent is on another syllable. Why e interchanges with o is not clear. The
