Old Norse has three categories of verbs (strong, weak, & present-preterite) and two categories of nouns (strong, weak). Conjugation and declension are carried out by a mix of inflection and two nonconcatenative morphological processes: umlaut, a backness-based alteration to the root vowel; and ablaut, a replacement of the root vowel, in verbs.
Nouns, adjectives and pronouns are declined in four grammatical cases – nominative, accusative, genitive and dative, in singular and plural. Some pronouns (first and second person) have dual number in addition to singular and plural. The nouns have three grammatical genders – masculine, feminine or neuter - and adjectives and pronouns are declined to match the gender of nouns. The genitive is used partitively, and quite often in compounds and kennings (e.g.: Urðarbrunnr, the well of Urðr; Lokasenna, the gibing of Loki). Most declensions (of nouns and pronouns) use -a as a regular genitive plural ending, and all declensions use -um as their dative plural ending.
All neuter words have identical nominative and accusative forms, and all feminine words have identical nominative and accusative plurals.
The gender of some words' plurals does not agree with that of their singulars, such as lim and mund.
Morphophonology
Conditioned sound changes can cause some forms of a word to mismatch, or match in some words but not others. When speakers can't determine these conditions, but the effects remain, they are re-analyzed by speakers as rules for changing sounds during inflection, the morphophonology of the language. In this way, the history of a language affects its speakers.
During Proto-Germanic
Verner's law shifted Proto-Germanic /*h/ > /*g/ after an unstressed syllable. Afterwards, stress shifted to the first syllable in all words. In many Old Norse verbs, a lost /g/ reappears in the forms of some verbs, which makes their morphology abnormal, but remain regular because the forms containing /g/s are the same for each verb they appear in. ex.: Proto-Germanic *slōhúm > *slōgúm (we struck) had an unstressed first syllable, but the corresponding singular, *slṓh (I struck), had only a stressed syllable. These became Old Norse slógum and sló.:1
Before Old Norse
Umlaut was originally an assimilation of root vowels to suffixes having the front phonemes (i-umlaut) and the back phonemes (u-umlaut) in Proto-Germanic. The suffixes were not on all forms of the same words, so when the suffixes underwent syncope during the transition into Old Norse, the remaining umlaut of the vowel indicated what the suffix had before. From then on speakers would alternate the vowel as an act of inflection.
Verbs
Verbs are conjugated in person and number, in present and past tense, in indicative mood, imperative, and subjunctive mood. There are elements of repetition and minor variation in the inflections, but the type of verb also determines which patterns are present. The subjunctives show the largest and widest spread pattern among the inflections, with both strong and weak classes ending subjunctives (past and present) with ek/þú/þat -a/-ir/-i, vér/þér/þau -im/-ið/-i, except for a minor variation in the 3rd, 4th and 5th strong conjugations.
The active participle is used to form a gerund or a verbal noun with weak masculine singulars but strong masculine plurals in r, or else with weak neuter declension. As a plain participle, it is a weak adjective. The participle appears in two genders within the same verse in Hávamál: "gínanda úlfi / galandi kráku." The general sense of the noun is of the English suffix -er or of being able to perform the action. The plural as a prefix, ęndr-, is equivalent to the English and Latin prefix re-.
The case of the object of an Old Norse verb is lexically assigned, meaning that the case is determined on a per-verb basis. Most verbs take an accusative object, but some, such as gefa (give) have primary and secondary objects in the accusative and dative, while still others have nominative, genitive, or dative direct objects.
Strong verbs
Strong verbs, unlike weak verbs, are conjugated by ablaut, a process that replaces, rather than modifies, their root vowel. The English sing uses ablaut to conjugate to sang in the past tense and sung as the past participle. Like weak verbs, strong verbs use inflections and umlaut, but they rely on them much less to distinguish forms and conjugations. While the strongs' umlaut and inflectional patterns are largely the same from verb to verb, there are different sets and numbers of vowels involved in ablaut, and so their patterns are used to classify the strong conjugations.
If there are 2 vowels in the pattern (as in the 6th & some 7th conjugation patterns), the 2nd is used for all the past forms. If there are 3, the 2nd vowel is used for the indicative past singulars, & the 3rd for the other past tenses. The 1st vowel is used for the remaining forms: the infinitive, present forms, and imperative, and usually the past participle of 3-vowel words. However, some 3-vowel words have a 4th vowel appearing only in the participle.
The past participle of strong verbs follows the pronominal declension of hit, though unlike the definite suffix the participle is inherited from Proto-Germanic.
1st: í, ei, i, i/e 2nd: ú/jú/jó, au, u, (o) rísa (í, ei, i, i) (rise) bjóða (jó, au, u, o) (bid) Inf rís-a Imp rís Pr P rís-andi Inf bjóð-a Imp bjóð Pr P bjóð-andi Pa P Pa P N ris-it M ris-inn F ris-in N boð-it M boð-inn F boð-in ek þú þat vér þér þau ek þú þat vér þér þau Pr T Ind rís rís-s rís-um rís-ið rís-a býð býð-r bjóð-um bjóð-ið bjóð-a Subj rís-a rís-ir rís-i rís-im rís-i bjóð-a bjóð-ir bjóð-i bjóð-im bjóð-i Pa T Ind reis reis-t reis ris-um ris-uð ris-u bauð baut-t bauð buð-um buð-uð buð-u Subj ris-a ris-ir ris-i ris-im ris-ið ris-i byð-a byð-ir byð-i byð-im byð-ið byð-i
The 3rd, 4th and 5th conjugations have an i, rather than an a, in the 1st person subjunctive past ending. Third conjugation words ending in n, g, or k have a u for their past participles' root vowel. The jas of the 3rd conjugation are due to breaking. The 4th and 5th conjugations are identical except in the past participle, where the 4th conjugation normally has o and the fifth conjugation e. Generally, 3rd conjugation stems have two consonants following the vowel; 4th conjugation stems have a single sonorant consonant (l, r, m or n) following the vowel; and 5th conjugation stems have a single consonant that is not a sonorant.
3rd: i/e/ja, a, u, (u/o) 4th: e/o, a, á, (u/o/ó) 5th: e/i, a, á, (e) brenna (e, a, u, u) (burn) bera (e, a, á, o) (bear/carry) gefa (e, a, á, e) (give) Inf brenn-a Imp brenn Pr P brenn-andi Inf ber-a Imp ber Pr P ber-andi Inf gef-a Imp gef Pr P gef-andi Pa P Pa P Pa P N brunn-it M brunn-inn F brunn-in N bor-it M bor-inn F bor-in N gef-it M gef-inn F gef-in ek þú þat vér þér þau ek þú þat vér þér þau ek þú þat vér þér þau Pr T Ind brenn brenn-r brenn-um brenn-ið brenn-a ber ber-r ber-um ber-ið ber-a gef gef-r gef-um gef-ið gef-a Subj brenn-a brenn-ir brenn-i brenn-im brenn-i ber-a ber-ir ber-i ber-im ber-i gef-a gef-ir gef-i gef-im gef-i Pa T Ind brann brann-t brann brunn-um brunn-uð brunn-u bar bar-t bar bár-um bár-uð bár-u gaf gaf-t gaf gáf-um gáf-uð gáf-u Subj brynn-i brynn-ir brynn-i brynn-im brynn-ið brynn-i bær-i bær-ir bær-i bær-im bær-ið bær-i gæf-i gæf-ir gæf-i gæf-im gæf-ið gæf-i
The 6th conjugation is cognate with English's take/took/taken conjugation. The 7th conjugation is a heterogenous category. Its ablaut patterns include a/á, e/é; au, jó; a, jó, jo; and ý, jó, ú.
6th: a, ó 7th: Various fara (a, ó) (go) gráta (á, é) (weep) Inf far-a Imp far Pr P far-andi Inf grát-a Imp grát Pr P grát-andi Pa P Pa P N far-it M far-inn F far-in N grát-it M grát-inn F grát-in ek þú þat vér þér þau ek þú þat vér þér þau Pr T Ind fęr fęr-r fǫr-um far-ið far-a græt græt-r grát-um grát-ið grát-a Subj far-a far-ir far-i far-im far-i grát-a grát-ir grát-i grát-im grát-i Pa T Ind fór fór-t fór fór-um fór-uð fór-u grét grét-st grét grét-um grét-uð grét-u Subj fœr-a fœr-ir fœr-i fœr-im fœr-ið fœr-i grét-a grét-ir grét-i grét-im grét-ið grét-i
Verbs in -ra
The -ra conjugation consists of strong verbs with weak preterites that use an r rather than a dental in their inflection. These arose as contractions of reduplicated verbs. They correspond to modern Icelandic ri-verbs. When the pre-contraction form of the verb contained a velar, it persisted in the past indicative plurals, past subjunctives, and past participle, and the verb assumed the characteristics (ablaut, inflection) of normal strong conjugation. Alternate, regularized past-tenses for these were also in use in some dialects, with an -ø-r or -e-r format. Verbs like kjósa and snúa follow the ú/jú/jó, au, u, (o) ablaut pattern, and verbs like slá follow the a, ó ablaut.
-ra snúa (turn) Inf snú-a Imp snú, snúðú Pr P snú-andi Pa P N snú-it, snør-it M snú-inn snør-inn F snú-in snør-in ek þú þat vér þér þau Pr T Ind sný sný-r, snýrðu sný-r snú-m snú-ið snú-a Subj snú-a snú-ir snú-i snú-im snú-i Pa T Ind snø-ra snø-rir snø-ri snø-rum snø-ruð snø-ru Subj snø-rim snø-rið snø-ri
The forms of slá without the g have absorbed said consonant, lengthening the vowel in the process. When this process is taken into account, the conjugation can be seen as that of a regular verb with an a, ó ablaut pattern. The -ø-r past tense forms were used in some dialects, with sløri and sløru as attested forms, but was rare in writing.
-ra: Velar stem slá (a, ó) (strike, slay) Inf slá Imp slá, sláðú Pr P slá-ndi Pa P N slęg-it M slęg-inn F slęg-in ek þú þat vér þér þau Pr T Ind slæ slæ-r slá-(u)m slá-ið slá Subj slá slá-ir slá-i slá-im slá-i Pa T Ind sló sló-(tt-(ú)) sló slóg-um slóg-uð slóg-u Subj slœg-a slœg-ir slœg-i slœg-im slœg-ið slœg-i
Weak verbs
Weak verbs distinguish the tenses of the indicative and subjunctive primarily by adding a suffix with a dental (t, d, or ð). This is the primary mode of distinction of tenses, in contrast with the radical vowel changes characteristic of the strong verbs. Preceded by the dental, the subjunctive past tense endings take the form of their present tense endings, changing the inflectional vowel to i in the plural. The indicative forms take the subjunctive forms, changing the inflectional vowel to u in the plural. The dental is preceded by an a in some verbs, causing the past tenses to become trisyllabic.
There are three primary conjugations, corresponding approximately to the first three classes of weak verbs in Gothic. The Proto-Germanic and Gothic Class IV weak verb, with a *-n(ō)- suffix, has been incorporated into the second conjugation in Old Norse.
First conjugation The first weak conjugation has an -i/j- suffix, which triggers i-umlaut of the stem. As in other Germanic languages, there are two subclasses, depending on whether the stem is short (consisting of a short vowel followed by at most one consonant) or long (containing a long vowel or diphthong, or followed by two or more consonants). The differences are due to Sievers' law, which caused the suffix to assume the form *-j- after short syllables but *-ij- after long syllables. The long *-ij- suffix subsequently disappeared when followed by a vowel that remained in Old Norse (except after k, g or a vowel, as in fylgja "to follow"), but betrays its former presence by i-umlauting the stem syllable.