Weak & Strong
Both weak and strong verbs were used in Old English. The past and past participles of weak verbs were usually formed by adding dental suffixes to the present tense stem (as in the Modern English 'laugh', 'laughed', 'laughed'). For the strong verbs, the stem vowels are changed (as in 'sing', 'sang', 'sung').
The strong Anglo-Saxon verbs still in use today are easily recognized by the vowel changes. (They also make English difficult to learn as a foreign language!) They are somewhat complicated by the seven different classes of vowel gradations that were used. Of these, some were regular and some were not. The following are examples of each class still in use:
Class 1: 'shine'
Class 2: 'creep'
Class 3a: 'thresh'
Class 3b: 'fight'
Class 3c: 'help' (archaic past tense 'holp')
Class 3d: 'yield'
Class 3e: 'sing'
Class 4: 'bear'
Class 5: 'see'
Class 6: 'slay'
Class 7a: 'know'
Class 7b: 'fall'
Some weak verbs also are still in use, as well. Most verbs created since the Anglo-Saxon period, as well as those borrowed from other languages, are treated as weak. A few of them also changed their stem vowels in the past and past participle. Notable examples of these exceptions still in use include 'seek', 'sell', 'think', 'bring', 'think', and 'buy'.
The important verb ' to be' is anomalous.
The only two tenses of Old English verbs were present and past (preterite).
Indicative, subjunctive, and imperative moods were used. The subjunctive mood has survived primarily with the verb " to be" Present and past participles, as well as two infinitives (one without 'to'; the other inflected and with "to') were also used.
Singular and plural verbs were used.
Verbs in three persons were used in the singular of the present and past indicative. All plurals and the subjunctives were the same throughout.
With but one exception, only the active voice was used in Old English.