1. Middle English period great change Middle English Verbal System

Suffixless weak verbs are mainly verbs formed from Latin past participles. As the Latin past participle was already felt to contain a past suffix, the addition of a suffix was deemed redundant.

Irregular weak verbs are verbs that for whatever reason do not fit into one of the above classes.

Strong verbs
form their past through modification of a verb's stem vowel. Some weak verbs also undergo changes in the stem vowel, but in strong verbs, this change reflects Indo-European ablaut. Middle English retains the seven classes that comprised the strong verb system in earlier Germanic languages, each with their own stem vowel alternations. Verbs influencing verbs of different classes, phonetic changes, and levelling within paradigms, each of which may or may not occur within any given member of a class, have led to the classes starting to lose their coherence (a process that continues in modern English). However, as a whole, strong verbs have remained a coherent category, with unique features like their characteristic vowel alternations, past participles in -en, and lack of the second-person suffix -est in the past.
terite-present verbs form their present from endings that other verbs use to form their past (hence their name); this means that unlike strong or weak verbs, they usually have a different vowel in the present singular than they do in the infinitive. Their past forms are formed like a weak verb's, though they may sometimes have an ablaut vowel that is distinct from the infinitive and the present. In Middle English, the preterite-presents are subject to increasing influence from strong and weak verbs; the alternations between the present singular and infinitive vowels tend to be leveled, and most acquire weak past participles on the model of their weak past. The class only retains its coherence due to the conspicuous lack of the third-person ending -th (or -s in some dialects), but even that is occasionally lost.
As well as their inflectional distinctiveness, preterite-presents are also syntactically unusual; most of them are modal verbs or auxiliary verbs (those that aren't tend to become weak verbs), and they often lack certain forms (i.e. they are "defective verbs").
There are less than 20 preterite present verbs; the principal ones are cunnen, douen, durren, moten, mowen, schulen, tharen and witen. At an early stage unnen was lost, while owen became a weak verb later in the Middle English period. There is one borrowed preterite-present: mone, from Old Norse (its native cognate monen is a weak verb in Middle English, despite having a preterite-present origin).