This law has, however, many exceptions in MHG. owing to levelling having taken place with the infinitive, present indicative and preterite singular, as risen, gerisen beside rirn, gerirn.
The same interchange of consonants exists between strong verbs and their corresponding causative weak verbs, as līden, to go: leiten, to lead; hāhen, to hang: hengen, to hang (trans.); ge-nësen, to be saved: nern, to save; and in nouns, &c., as hof (gen. hoves), court: hübesch, courtly; tōt (gen. tōdes), death: tōt (gen. tōtes), dead; swëher, father-in-law: swiger, mother-in-law; hase: English hare.
[§ 31.] The doubling of consonants took place under certain well-defined rules partly in prim. Germanic and partly in prim. West Germanic, see the Author’s Hist. Germ. Grammar, §§ 202, 213-14. Examples of words which had double consonants in prim. Germanic are: kopf, head; napf (OE. hnæp, gen. hnæppes), basin; boc (OE. bucca), buck, gen. bockes; rinnen, to run; swimmen, to swim; vol (gen. volles), full; vërre, far; gewisser, certain.
The chief cases in which double consonants arose in prim. West Germanic were:—
[1.] The assimilation of ƀn, ʒn, pn to bb, gg, pp = MHG. pp, ck (gg), pf, as knappe: knabe, boy; rappe: rabe, raven; rocke: rogge, rye; tropfe, drop: triefen, to drip.
[2.] p, t, k were doubled before a following r or l. The doubling regularly took place in the inflected forms, and was then extended to the uninflected forms by levelling, as apfel (OE. æppel), apple; kupfer (Lat. cuprum), copper; bitter (Goth. báitrs), bitter, see [§ 23 note]; lützel (OS. luttil), little; acker (Goth. akrs), field; wacker (OE. wæccer), watchful. See [§ 23, 2].
[3.] All single consonants, except r, were doubled after a short vowel when there was originally a j in the next syllable. The bb, dd, gg; pp, tt, kk, which thus arose, became pp (bb), tt, ck (gg); pf, tz, ck in MHG. (§§ [23], 2, 26), as sippe (sibbe), Goth. sibja, relationship; bitten, later biten, Goth. bidjan, to request; tretten (wv.): trëten (sv.), to tread; brücke (brügge), bridge; ecke (egge), edge; mücke (mügge), midge; rücke (rügge), ridge, back. schepfen, Goth. skapjan, to create; hitze, heat: heiȥ, hot; netzen, to wet: naȥ, wet; setzen, Goth. satjan, to set; sitzen, to sit: pret. saȥ, p.p. gesëȥȥen; decken, to cover: dach, cover; lücke, gap: loch, hole. zellen, later zeln, to count: zal, number. vremmen, later vremen (OE. fremman), to perform. henne, hen: hane, cock.
In MHG. the double consonants in verbs were often simplified through the levelling out of forms which regularly had a single consonant, e.g. regular forms were: vremmen, to perform, sing. vremme, vremes(t), vremet, pl. vremmen, vremmet, vremment, pret. vremete, p.p. gevremet, then the stem-form with single m was levelled out into all the forms, and similarly with many other verbs, as denen, to stretch; seln, to hand over; weln, to choose; wenen, to accustom; legen beside lecken (leggen), to lay; and the strong verbs biten, to beg; ligen beside licken (liggen), to lie down.
[§ 32.] Double consonants were simplified:—
[1.] When they became final, as boc, buck, kus, kiss, man, man, schif, ship, stum, dumb, vël, hide, beside gen. bockes, kusses, mannes, schiffes, stummes, vëlles; pret. maȥ, ran, traf, beside mëȥȥen, to measure, rinnen, to run, trëffen, to hit.