Proto-Germanic verbs are conjugated according to:
- Person (1st, 2nd, 3rd)
- Number (singular, dual, plural)
- Tense (present, past)
- Mood (indicative, subjunctive, imperative)
- Voice (active, passive)
Not all combinations of these categories exist. There is no 3rd person dual form, and the passive voice has no forms for the past tense or imperative mood. Intransitive verbs also lack passive forms for semantic reasons. In addition to these combinations, there are also three non-finite forms: an infinitive and a present (active) and past (passive) participle.
Proto-Germanic verbs can be divided into three broad groups: strong, weak and preterite-present. These differ in how the tenses are formed, but are otherwise identical in their inflection. In addition, some verbs are irregular and follow non-standard patterns of inflection, although they are generally still analogous to the other three categories.
Strong verbs display their tense through ablaut and/or reduplication; the past tense shows a different stem than the present. There are seven classes of strong verb. The first six classes form the past tense with ablaut alone, and the seventh class forms it through reduplication. However, there are some class 7 strong verbs that have both ablaut and reduplication.
|Class||present||past sg. indic.||past general||past ptc.||Category|
|1||-ī-||-ai-||-i-||-i-||Category:Proto-Germanic class 1 strong verbs|
|2||-eu- (-iu-)||-au-||-u-||-u-||Category:Proto-Germanic class 2 strong verbs|
|3a||-i-||-a-||-u-||-u-||Category:Proto-Germanic class 3 strong verbs|
|4||-e- (-i-)||-a-||-ē-||-u-||Category:Proto-Germanic class 4 strong verbs|
|5||-e- (-i-)||-a-||-ē-||-e-||Category:Proto-Germanic class 5 strong verbs|
|5 j-present||-i-||-a-||-ē-||-e-||Category:Proto-Germanic class 5 strong j-present verbs|
|6||-a-||-ō-||-ō-||-a-||Category:Proto-Germanic class 6 strong verbs|
|6 j-present||-a-||-ō-||-ō-||-a-||Category:Proto-Germanic class 6 strong j-present verbs|
|7a||?||red||red||?||Category:Proto-Germanic class 7 strong verbs|
|7b||-ē-||-ō- + red||-ō- + red||-ē-|
|7a j-present||?||red||red||?||Category:Proto-Germanic class 7 strong j-present verbs|
If the vowel of the present contains -e-, it becomes -i- when the following ending begins with -i-; this occurs in the 2nd and 3rd person singular forms, and the 2nd person plural form.
A few strong verbs in classes 5, 6 and 7 are so-called j-present verbs. These verbs show a j-suffix in the present tense, and therefore inflect like the class 1 weak verbs.
Phonetic processes in strong verbs
Reduplication in class 7 strong verbs is formed by taking the initial consonant of the stem and prefixing it to the stem, with -e- in between. If the stem begins with s- followed by another consonant, both consonants are reduplicated. The initial s- of the original stem undergoes Verner's law alternation when the reduplicating prefix is added, and becomes -z- (as in Gothic saizlēp for the past tense of slēpan, and the four Icelandic ri-verbs).
Verner's law alternations (f-b, þ-d, h-g, hw-gw, s-z) generally occur in the final stem consonant of all strong verbs. The first and second principal parts show the voiceless alternant, and the third and fourth show the voiced alternant. This phenomenon is known as grammatical change or grammatischer Wechsel, and survives in several West Germanic languages up to today (as in English was and were).
The alternations are somewhat more complicated in verbs containing labiovelars (hw, kw or gw), since these underwent further changes in Germanic. Generally, labiovelars are delabialised and become h, k or g when they stand next to -u-, or are preceded by -un-. This applies both to stem-initial and stem-final labiovelars, and can be seen in *kwemaną, where the -u- of the past stem triggers the change.
Since gw, when it had not been delabialised at an earlier stage, generally became w in Germanic unless preceded by n, verbs ending in gw or hw (which becomes gw through Verner alternation) are particularly complex. If gw is preceded by n, it remains as such but the usual delabialisation rules apply. This is seen in *þrinhwaną. If gw is not preceded by n, then it becomes w unless next to u, in which case it is delabialised and appears as g instead. The verb *sehwaną demonstrates this three-way consonant alternation.
The 2nd person singular past indicative ending -t generally triggers assimilation of the preceding consonant according to the Germanic spirant law:
- bt, pt > ft
- dt, tt, þt > st
- gt, kt, hwt > ht
Weak verbs form the past tense with a suffix in -d-, or sometimes -t-. There are four main classes of weak verb, which differ in the vowels that follow the verb stem.
Suffixless weak verbs
This is a relic class consisting of only a few verbs. Their present tense is identical to that of strong verbs, the past tense had no linking vowel.
This class consists of verbs ending in -(i)janą, and has a past tense in -id-. The present tense suffix varies between -ja/ija- and -i/ī-.
A few irregular verbs in this class are j-presents, and have the suffix only in the present tense, analogous with the strong j-presents. Their past tense has -t-, with the preceding consonant assimilating to the suffix according to the Germanic spirant law.
This class consists of verbs ending in -ōną, and has a past tense in -ōd-. The present tense suffix is always -ō-.
This class has two subclasses, which are mostly different in the forms. The only feature they share is the suffix -ai- in some of the forms. However, the two subclasses merged into one in all the later languages for reasons that are not quite clear.
The first and larger subclass has an infinitive in -(i)janą and a past tense in -d- with no linking vowel. The present tense suffix varies between -ja/ija- and -ai-. These verbs are statives, and indicate being in a particular state.
The second subclass has an infinitive in -āną and a past tense in -ād-. The present tense suffix varies between -ā- and -ai-. These verbs are factitives, similar to the first class of weak verbs.
This class has been notoriously difficult to reconstruct, but some details are known. The infinitive ended in -naną, and the past tense was formed with -nōd-. The present tense forms are uncertain, but probably varied between -ō- and -a-. These verbs are inchoatives, and indicate a change of state or the process of coming into that state. As a result, they are always intransitive, and have no passive forms or a past participle.
Preterite-present verbs are a small group of originally perfect verbs whose present tense forms appear like the past tense forms of strong verbs. Because of this, they have no passive forms. Like strong verbs, they show ablaut, but the ablaut patterns of the present are those of the strong past. Therefore, principal part 1 does not appear, and principal part 2 appears in the present singular indicative. The past tense is formed like weak verbs, with no linking vowel, and often shows the effects of the Germanic spirant law.
The future tense is often expressed using the present tense, but may be formed using the auxiliary verb *skulaną.
Modality is generally expressed using various preterite-present verbs. *skulaną indicates an absolute requirement, or even inevitability. This explains its use for forming the future tense. *þurbaną expresses a strong need or requirement. *maganą is used to express a possibility within the circumstances. *kunnaną by comparison indicates a possibility by one's own ability or knowledge. *mōtaną is used for permission, where the possibility is determined by the wishes of another person. *wiljaną meanwhile expresses one's own wishes.