√bhereu̯ ‘boil’: FV *bheru̯‑, see iv above;—VR *bhru- > W. brwd ‘hot, fervent’, Lat. dē-frŭ-tum ‘new wine boiled down’.
*qu̯etu̯er- ‘four’: RF° *qu̯ₑtu̯or- > Lat. quattuor;—FR *qu̯etuₑr- > W. pedwar, Ir. cethir, Gk. τέτταρες;—RL° *qu̯ₑtu̯or- > Skr. catvā́raḥ, Goth. fidwor; FR (before cons.) *qu̯etu̯r̥- > Gk. τετρα‑, becoming by viii (1) *qu̯etru- it gives Gaul. Petru‑, W. pedry- as in pedry-fan.
(5) Long diphthongs must represent radical disyllables, and their reduced grades can only be explained from the disyllabic forms. Thus ēi̯ must be FV of *eə̯ei̯ or *eə̯ai̯ (ei/ai v (2)); the R of the first syll. is ə which vanishes before a vowel, leaving ei or ai (properly VF of *eə̯ei̯ or *eə̯ai̯); if the second is reduced we get ii̯, before a cons. i (properly VR of *eə̯ei̯ or *eə̯ai̯). We know that ēi̯ interchanges in roots with ei̯ē or ei̯ā; this implies a metathesis of the sonants, for the latter forms represent *ei̯eə̯ or *ei̯aə̯; the RR of these is *ii̯ə which gives ī, see vii (2). Thus we have as reduced grades of ēi̯ the forms ei or ai, i(i̯), ī; for convenience these may be distinguished thus: R₁ₑ ei, R₁ₐ ai, R₂ ii̯, i, R₃ ī. The same principle applies to the long u̯-diphthongs. [It has been assumed that ai is əi̯ (with ə as R of ē), but Skr. has ay for it, whereas ə is i in Skr. Besides, we should expect əi̯ like ₑi̯ to give *ii̯, as perhaps it does, for ii̯ may also be for *əi̯ RV of *eə̯ei̯.] Examples :
√sēi̯- ‘late, long’: F *sēi̯- > Skr. sāyám ‘evening’, before cons. *sē- > Lat. sērus, W. hir ‘long’, Ir. sīr;—R₁ₑ *sei- > W. hŵyr ‘late’ (< *sei-ros), hŵy ‘longer’, Ir. sīa (< *seison < *sei-isōn);—R₂ *si- > W. hyd ‘length’ (< *sit‑);—R₁ₐ *sai- > W. hoedl ‘lifetime’, Lat. saeculum ‘age’, both < *sai-tlo‑m § 75 i.
√u̯erēi̯- ‘laugh (at), shame’: VR₂ *u̯ri- > *u̯ri‑zd- whence Lat. rīdeo, Skr. vrīḍ-ā ‘shame’;—(VF *u̯rē- or else) VR₃ *u̯rī- > Kelt. *u̯rī‑t- > W. gw̯rīd ‘blush’;—RR₂ *u̯ₑri- > *u̯aritā in W. dan-wared ‘to mimic’;—RR₂ *u̯ₑrii̯- > W. gw̯arae ‘play’ § 75 v (4).—From √u̯erē- (without i̯): RR *u̯ₑrə- > *u̯arat- > W. gw̯arad-w͡yẟ ‘shame’ (by dissim. for *gwarad-rw͡yẟ);—R(R) *u̯ₑr’- > *u̯ar‑t- > W. gwarth ‘shame’; *s‑u̯ar‑d- > W. chwarẟ ‘laughs’; *s‑u̯ar-tīn-ī > W. chwerthin ‘laughter’ § 203 vii (3).
viii. (1) Certain combinations produced by the above laws are unstable; thus u̯r̥ is liable to become ru, as in *qu̯etru- vii (4); and u̯ₑr may become ur as in *dhur- for *dhu̯ₑr‑: *dhu̯or‑, § 91 i. While u̯ₑ, lₑ, rₑ, etc., may remain and give u̯a, la, ra, etc., in Kelt., they may be, and oftenest are, reduced to u, l̥, r̥, etc. Hence we are not obliged to postulate eue, ele, ere, etc., where there is no evidence of the first e in surviving forms. Thus:
√su̯ep- ‘sleep’: F *su̯ep-no- > Lat. somnus (< *su̯epnos), Skr. svápnaḥ ‘sleep, dream’;—R *sup-no- > Gk. ὔπνος, W. hun ‘sleep’, Ir. sūan.
√plethē‑: RR *pl̥thə- > Gk. πλάτα-νος, Gaul. ‑λιτα-νο‑ς, O.W. lita‑n, W. llyda‑n ‘broad’; FV *pleth- > Skr. práth-aḥ ‘breadth’, W. lled ‘breadth’;—RV *pl̯th- > W. llys ‘court’ § 96 ii (5), Gk.
