In Germanic languages, weak verbs are by far the largest group of verbs, which are therefore often regarded as the norm, though historically they are not the oldest or most original group.
For other aspects of the verb in Germanic languages see the article Germanic verb.
In Germanic languages, weak verbs are those verbs that form their preterites and past participles by means of a dental suffix, an inflection that contains a /t/ or /d/ sound or similar. For example: to love - loved to say - said to send - sent to buy - bought to set - set to lean - leaned or leant
For comparative purposes we may refer to this generally as a dental, although in some of the languages, including English, /t/ and /d/ are alveolar rather than dental consonants. In English, the dental is a /d/ after a voiced consonant or vowel, and a /t/ after a voiceless consonant, though English uses the spelling in in most cases, regardless of pronunciation. In German and Dutch, terminal devoicing means that final consonants are never voiced, so the pronunciation /d/ does not occur. Nevertheless, Dutch distinguishes the letters and regularly as though the originally voiced consonants were still voiced. (See Dutch spelling for the 't kofschip rule.) German on the other hand knows only spellings in . In Icelandic, the dental has become a voiced dental fricative /ð/, as it was in some verbs in Old English. In Afrikaans it has disappeared altogether.
The weak conjugation of verbs is an innovation of Proto-Germanic (unlike Germanic strong verbs, which go back to Proto-Indo-European). The origin of the dental suffix is uncertain. One theory is that it evolved out of a periphrastic construct with the verb to do: Germanic lubōjana dēdo ("love-did") → lubōdo → Old English lufode → loved. This would be analogous to the way that in Modern English we can form an emphatic past tense with "did": I did love. Another theory is that it came from a past participle ending, a final -daz from PIE -tos (cf Latin amatus), with personal endings added to it at a later stage. Both theories are disputed because of their inability to explain all the facts.
Weak verbs should be contrasted with strong verbs, which form their past tenses by means of ablaut. All the original Indo-European verbs which came into Germanic as verbs were once strong. However, as the ablaut system is no longer productive except in rare cases of analogy, almost all new verbs in Germanic languages are weak, and the majority of the original strong verbs have become weak by analogy. In some cases a verb has become weak in the preterite but not in the participle, or (rarely) vice versa. These verbs may be thought of as "semi-strong" (not a technical term). Dutch has a number of examples of this: wassen waste gewassen ("to wash") jagen joeg gejaagd ("to hunt")
In Germanic, one very productive source of new verbs was the derivation of new verbs with causative meanings from existing verbs, resulting in many pairs of related strong and weak verbs: the original strong verb fall fell fell has a related weak verb fell felled felled, which means "to cause (a tree) to fall"; strong sit sat sat and lie lay lain are matched with weak set set set and lay laid laid, meaning "to cause something to sit" or "lie" respectively. Occasionally semantic shifts make these pairs difficult to recognise. German strong leiden litt gelitten ("to suffer") has the derived weak verb leiten ("to lead"), which makes sense when one realises that leiden originally meant "walk, go" and came to its present meaning through the idea of "undergoing" suffering.
In the medieval Germanic languages, a number of different classes of weak verbs had to be distinguished, according to the consonants in the stem. Class 1 is known as the -jan conjugation, because their development was influenced by a /j/ in Germanic, which however is only attested in Old Saxon. In Old English, class 1 weak verbs commonly had preterites ending in -ede. This group commonly experienced consonant doubling in the infinitive caused by West Germanic Gemination. Class 2 weak verbs typically ended in -ode in Old English. Besides these two main classes there were several smaller ones.
Weak verbs are often thought of as having a regular inflection, but not all weak verbs are regular verbs; some have been made irregular by ellipsis or contraction, such as hear ~ heard; while others are merely irregular due to the eccentricities of English spelling, such as lay ~ laid. In German, verbs ending in -eln or -ern have slightly different inflection patterns. There are many other examples. The Preterite-present verbs are in a sense weak verbs with very significant irregularities; but usually they are not bracketed under weak verbs.
One particularly interesting category of irregular weak verb is the so-called rückumlaut verb. This is discussed in the article on Germanic umlaut under the section "Umlaut in Germanic verbs". An original -j- in the inflection caused the whole of the present stem (including the infinitive) to experience a fronting of the stem vowel, though the past tense retains the back vowel. Another irregularity is a consonant alternation sometimes referred to by the German word Primärberührung, which looks superficially like Grammatischer Wechsel but in fact results from the phenomenon of the Germanic spirant law in early Germanic. In effect this is a process of assimilation of the plosive at the end of the stem caused by contact with the dental suffix. Both Rückumlaut and Primärberührung are observable in the verb to think: * English: think thought * German: denken dachte gedacht Some grammar books use the term "mixed verb" to describe these. This rests on the misconception that these verbs display both ablaut and a dental suffix, and are therefore at once strong and weak. But the vowel change is not ablaut.
The term "weak verb" was originally coined by Jakob Grimm and in his sense refers only to Germanic philology. However, the term is sometimes applied to other language groups to designate phenomena which are not really analogous. For example, Hebrew irregular verbs are sometimes called weak verbs because one of their radicals is weak.
