The standard descriptions

It is widely acknowledged among historical linguists that between the ninth and the thirteenth centuries English stressed vowels under went widespread quantity changes. The established way of describing these alterations is in terms of four distinct sound changes. The first of them, which has become known as Homorganic Lengthening (from now on HOL), seems to have made short vowels long, if they were followed by certain consonant groups (namely: mb, nd, ng, ld, rd, rs, rn, rð) – unless those groups were themselves followed by a consonant. It turned bindan into bīndan, cild into cīld, or climban into clīmban, to give a few examples. The second change is supposed to have made long vowels short, if they were followed by a group of two consonants. (Homorganic groups did not trigger the change, however; nor did groups that occurred at the beginning of words, such as: pl, pr, cl or tr.) This change, which is called Shortening before Consonant Clusters (SHOCC), is taken to have been behind such changes as that of kēpte into kepte, dūst into dust or fīfta into fifta. By the third change, then, long vowels are supposed to have been shortened if they occurred in the antepenultimate syllables of wordforms: suþerne and erende are thus said to have replaced sūþerne and ērende, for example. This change is commonly called Trisyllabic Shortening (TRISH). The fourth process, finally, is believed to have lengthened short vowels, if no consonant followed them within the same syllable. It is said to have turned maken into māken, weven into wēven or hopen into hōpen and is known as Open Syllable Lengthening (OSL).