table at List of English irregular verbs. Weak verbs Some other irregular verbs derive from Germanic weak verbs, forming past tenses and participles with a -d or -t ending (or from originally strong verbs that have switched to the weak pattern). The weak conjugation is also the origin of the regular verbs in -ed; however various historical sound changes (and sometimes spelling changes) have led to certain types of irregularity in some verbs. The main processes are as follows (some verbs have been subject to more than one of these). Some weak verbs with long vowels in their present tense stems (such as keep) took a short vowel in the past tense and past participle (kept). In some weak verbs ending in a final -t or -d, this final consonant coalesced (contracted) with the weak past ending to leave a single -t or -d in the past forms. Some verbs ending in l or n had their past ending irregularly devoiced to -t, and in a few verbs ending with a v or z sound (leave, lose), both that sound and the past ending were devoiced. (The regular ending -ed is also devoiced after voiceless consonants in regular verbs, as described under , but this is not now shown in the spelling – for example, the -ed in blessed and whipped is pronounced as a t, and these words were formerly written blest and whipt. The spelling -t following a voiceless consonant is retained for verbs that display an irregularity, as in kept and cost.) Some weak verbs continue the vowel shift called Rückumlaut ("reverse umlaut"). Details of the history of these verbs can be found under Germanic weak verb; those with -gh- in the spelling were also affected by the Germanic spirant law. A few weak verbs have undergone additional contractions or vowel shortenings in their past or present tense forms. A few verbs are regular in their spoken forms, but have irregular spelling. The irregular weak verbs (being in normal use) can consequently be grouped as follows: Verbs with vowel shortening: creep, flee, hear, keep, leap, shoe (when shod is used), sleep, sweep and weep. (Of these, creep, flee, leap, sleep and weep derive from verbs that were originally strong.) Verbs with vowel shortening and devoicing of the ending: deal, dream, feel, kneel, lean, leave, lose (originally strong) and mean. Some of the verbs in this and in