By gradation the vowels are related as follows:—
e (i, eo) .. a (æ, ea) .. u (o):—
bindan (inf.), band (pret.), bundon (they bound). beran (inf.), bær (pret.), boren (past partic.). ċeorfan (cut), ċearf (pret.), curfon (they cut), corfen (past partic.). bęnd (bond) = mutation of band, byr-þen (burden) of bor-en.
a (æ, ea) .. ǣ:—spræc (spoke), sprǣcon (they spoke), sprǣċ (speech).
a .. ō:—faran (to go), fōr (pret.), fōr (journey). ġe·fēra (companion) mutation of fōr.
ī .. ā .. i:—wrītan, wrāt, writon, ġe·writ (writing, subst.). (be)·līfan (remain), lāf (remains), whence by mutation lǣfan (leave).
ēo (ū) .. ēa .. u (o):—ċēosan (choose), ċēas, curon, coren. cys-t (choice). (for)·lēosan (lose), lēas (loose), ā·līesan (release), losian (to be lost). būgan (bend), boga (bow).
We see that the laws of gradation are most clearly shown in the conjugation of the strong verbs. But they run through the whole language, and a knowledge of the laws of gradation and mutation is the main key to O.E. etymology.
It is often necessary to supply intermediate stages in connecting two words. Thus lęċġan (lay) cannot be directly referred to liċġan (lie), but only to a form *lag-, preserved in the preterite læġ. So also blęndan (to blind) can be referred only indirectly to the adjective blind through an intermediate *bland-. Again, the root-vowel of byrþen (burden) cannot be explained by the infinitive beran (bear), but only by the past participle ġe·boren. In the same way hryre (fall sb.) must be referred, not to the infinitive hrēosan, but to the preterite plural hruron.
The vowel-changes in the preterites of verbs of the 'fall'-conjugation (1) feallan, fēoll, &c., are due not to gradation, but to other causes.
CONSONANTS.