Most academics classify all Old English verbs into four types: anomalous or basic, preterite-present, strong, and weak. The lemma form for an Old English verb is the infinitive, which typically ends with -an.
There were only two tenses in Old English, present and preterite. Either can modify into the subjunctive mood. The present tense is used for the future, with context determining which tense is meant. Auxiliary verbs such as willan also started to be used to indicate future during the Old English period.
Verbs conjugate through a mixture of inflectional suffixes and stem-modifications. Plural verb forms do not distinguish between persons.
These verbs show many irregularities, and tend to be old words. They are sometimes called "basic" verbs, because they are fundamental components of the language. Some of them are historically a blend of two or more different Germanic verbs.
There are only five: bēon, wesan, dōn, gān and willan.
Some Germanic verbs underwent a shift whereby their strong preterite-tense forms became reinterpreted as their present-tense forms. New "weak" endings were then used to form the new preterite tense. The present tenses of these verbs therefore resemble the preterite tense forms of strong verbs, below.
Many of the preterite-present verbs are important as modal verbs or auxiliary verbs.
Verbs are known as "strong" which form their preterite tenses by means of a change in the stem-vowel, i.e. by "ablaut". Many of these changes still exist in modern English, reflected in verbs such as sing (past tense sang, past participle sung).
There are seven classes of strong verbs in Old English, which are denoted on Wiktionary with Roman numerals. Each class has a different ablaut-series (though confusingly, there are three types of Class III).
Weak verbs are more predictable. They form their preterite tense by adding -de in the singular and -don in the plural. This is the root of the common English past-tense suffix -ed. Weak verbs are often formed from nouns, or are in general "newer" words.
There are three classes of weak verb, denoted on Wiktionary with Arabic numerals.
Class 1 weak verbs have an infinitive ending in -an or -rian. Third-person present singular ends in -eþ, and present plural ends in -aþ.
Class 2 weak verbs have an infinitive ending in -ian (except -rian, above). Their third-person present singular ending is -aþ, like Class 1 plurals. Class 2 present plurals end in -iaþ.
Class 3 weak verbs are more unpredictable, and often combine features of the first two weak classes. There are four Class 3 verbs: habban, libban, seċġan and hyċġan.