Adverbs are not inflected in Proto-Germanic, but they may have comparative and superlative degrees. They are often derived from adjectives, but there are also many adverbs that stand alone and are not derived, especially those indicating place.
Many adverbs could also be used as prepositions, and vice-versa. The distinction between them was not always clear. Therefore, most of what is explained here also applies to the formation of prepositions.
Adverbs could be formed from adjectives in several ways.
A single case exists where the derivation is suppletive: the adjective *gōdaz (“good”) has the adverbial form *wela (“well”).
A complex system of adverbs denoting place and time existed in Proto-Germanic. Such adverbs were generally formed from a base root, such as demonstratives and interrogatives (*þa-, *alja-, *hwa-), but also from existing adverbs.
Proto-Germanic had a system of directional adverbs formed from prepositions with suffixes attached to the root. These suffixes added directional meaning inherited from three grammatical cases reconstructed for Proto-Indo-European, although the allative case is less certain than the others.
| Preposition | Allative | Locative | Ablative |
|---|---|---|---|
| *in ("in") | *inn ("into") | *innai ("within") | *innanē ("from within") |
| *ub ("up, above") | *upp ("upward") | *uppai ("above") | *ubanē ("from above") |
| *uz ("out of") | *ūt ("outward") | *ūtai ("without") | *ūtanē ("from without") |
Like adjectives, Germanic adverbs could have a comparative and superlative form. They were formed similarly to those of adjectives. In general, a comparative or superlative adjective could be formed simply by dropping the case suffix: the comparative ended in -iz or -ōz, and the superlative in -ist(a) or -ōst(a). For adverb comparatives that did not derive from adjectives, the suffixes -iz and -ist(a) seem to have been the only ones in use. There were also several other suffixes which had specific uses and seemed to have become unproductive already in Germanic.
Adverbs, like adjectives, sometimes had comparative and superlative forms that were formed from different roots. In most cases, however, there is no corresponding positive degree, but the other two degrees are parallel to the corresponding adjectives.
| Adverb | Comparative | Superlative |
|---|---|---|
| *wela (“well”) | *batiz (“better”) | *batist (“best”) |
| "badly" | *wirsiz (“worse”) | *wirsist (“worst”) |
| "greatly, much, frequently" | *maiz (“more”) | *maist (“most”) |
| "little, seldom" | *minniz (“less”) | *minnist (“least”) |
| *laisiz (“less”) | *laisist (“least”) |