This is the workhorse of Icelandic noun declension: the strong masculine -ar plural class. Its members have a genitive singular in -s and a nominative plural in -ar, and they include a huge share of the everyday masculine vocabulary — hestur ("horse"), dagur ("day"), bíll ("car"), steinn ("stone"), hattur ("hat"), fiskur ("fish"). This page drills the full eight-cell paradigm until it is automatic, covers the -ll and -nn stems where the nominative's double letter simplifies in the other cases, and gives the u-umlaut (a → ö) that catches everyone in the dative plural. The single most useful fact about this class is at the end: it is the productive default, so an unfamiliar -ur masculine is a safe bet to decline this way.
The model: hestur
Here is hestur in full. Memorise this one paradigm and you have the skeleton of the entire class:
| Case | Singular | Plural |
|---|---|---|
| Nefnifall (nom.) | hestur | hestar |
| Þolfall (acc.) | hest | hesta |
| Þágufall (dat.) | hesti | hestum |
| Eignarfall (gen.) | hests | hesta |
The singular endings are -ur / – / -i / -s and the plural endings -ar / -a / -um / -a. Notice that the accusative singular hest is the bare stem (the nominative's -ur is gone), and that the accusative and genitive plural are identical (hesta). Those two coincidences — bare accusative singular, matching acc./gen. plural — are true of the whole class.
Hesturinn er fallegur.
The horse is beautiful. Nominative singular 'hestur' — the citation form with -ur.
Ég reið hesti alla leið heim.
I rode a horse all the way home. Dative singular 'hesti' after the verb 'ríða', which governs the dative — the -i ending.
Bóndinn á marga hesta.
The farmer owns many horses. Accusative plural 'hesta' after 'eiga' — note it is identical to the genitive plural.
The a-stem and its u-umlaut: dagur
Dagur ("day") declines exactly like hestur — until the dative plural. Because its stem vowel is a, the -um ending rounds it to ö: the dative plural is dögum, not dagum. Watch the table:
| Case | Singular | Plural |
|---|---|---|
| Nefnifall (nom.) | dagur | dagar |
| Þolfall (acc.) | dag | daga |
| Þágufall (dat.) | degi | dögum |
| Eignarfall (gen.) | dags | daga |
Two things to flag. First, the dative plural dögum shows the u-umlaut: any a in the stem rounds to ö whenever a u follows in the next syllable, so dag- + -um → dögum. The other plural cases keep the a (dagar, daga). Second — and this one is irregular — the dative singular is degi, with the a fronted to e. This is an old i-umlaut that survives in a small set of high-frequency words; you simply learn degi alongside dögum. Most -ar masculines have a plain dative singular in -i (hesti, fiski), so degi is the exception, not the rule.
Á góðum dögum förum við í gönguferð.
On nice days we go for a hike. Dative plural 'dögum' — the u-umlaut a → ö in action.
Það gerðist á þriðja degi.
It happened on the third day. Dative singular 'degi' — the irregular fronted form, not 'dagi'.
A cleaner a-stem is hattur ("hat"), which has the normal dative singular hatti and only the u-umlaut in the dative plural höttum: hattur, hatt, hatti, hatts / hattar, hatta, höttum, hatta.
Hann tók ofan hattinn þegar hann heilsaði.
He took off his hat when he greeted them. Accusative singular 'hatt' (here hattinn) — the bare stem, no -ur.
The -ll stem: bíll
A stem ending in -l doubles it in the nominative singular, giving -ll. In every other case the doubling vanishes and you work from the single-l stem bíl-:
| Case | Singular | Plural |
|---|---|---|
| Nefnifall (nom.) | bíll | bílar |
| Þolfall (acc.) | bíl | bíla |
| Þágufall (dat.) | bíl | bílum |
| Eignarfall (gen.) | bíls | bíla |
Note one extra wrinkle: the dative singular of bíll is the bare stem bíl (no -i), because -l stems of this shape don't take the dative -i. So the accusative and dative singular are identical here: bíl. The genitive singular is the expected bíls.
Ég á gamlan bíl.
I have an old car. Accusative singular 'bíl' — single l, no -ur.
Við komum á bíl, ekki með rútu.
We came by car, not by bus. Dative singular 'bíl' after 'á' — for this -ll stem the dative is the bare stem, with no -i.
Það eru of margir bílar á götunum.
There are too many cars on the streets. Nominative plural 'bílar' — the -ar that names the class.
The -nn stem: steinn
Exactly parallel to bíll, a stem in -n doubles to -nn in the nominative and reverts to the single-n stem stein- elsewhere. Unlike bíll, steinn does take the dative singular -i:
| Case | Singular | Plural |
|---|---|---|
| Nefnifall (nom.) | steinn | steinar |
| Þolfall (acc.) | stein | steina |
| Þágufall (dat.) | steini | steinum |
| Eignarfall (gen.) | steins | steina |
Barnið kastaði steini í tjörnina.
The child threw a stone into the pond. Dative singular 'steini' after 'kasta', which governs the dative.
Húsið er byggt úr steini.
The house is built of stone. Dative singular 'steini' after 'úr' — same form again.
Why this class is your default guess
Here is the practical payoff. The -ar plural class is productive — it is the live, growing pattern that absorbs new masculine words. Modern coinages and loanwords that end in -ur join it automatically: tölvupóstur ("email") → tölvupóstar, bíll itself (a 20th-century coinage) → bílar, strætó aside, most new -ur masculines pluralise in -ar. So when you meet an unfamiliar masculine ending in -ur and have no dictionary, your best bet is to decline it like hestur: bare accusative, dative -i, genitive -s, plural in -ar with -um in the dative.
Ég fékk þrjá tölvupósta í morgun.
I got three emails this morning. Accusative plural 'tölvupósta' — a modern compound declined like 'hesta'.
Hann er besti kennarinn — nei, fyrirgefðu, ég meinti einn af bestu kokkunum.
He's the best teacher — no, sorry, I meant one of the best cooks. Real backtracking speech; 'kokkunum' is the dative plural definite of 'kokkur', an -ar masculine.
This default is not a licence to guess everywhere — the -ir class (gestur → gestir) and the weak masculines (tími → tímar) are real and common. But for an opaque -ur noun with no other information, the hestur pattern is the percentage play.
Common Mistakes
❌ á góðum dagum
Incorrect — the dative plural rounds a → ö by u-umlaut: 'dögum', never 'dagum'.
✅ á góðum dögum
on good days — dative plural 'dögum'.
❌ Ég reið hest heim.
Incorrect — 'ríða' governs the dative, so you need the dative singular 'hesti', not the accusative 'hest'.
✅ Ég reið hesti heim.
I rode a horse home. Dative singular 'hesti' — don't drop the -i where it belongs.
❌ Keeping -ll in oblique cases: 'ég á gamlan bíll'
Incorrect — the double -ll is the nominative shape only; the accusative is the single-l stem 'bíl'.
✅ Ég á gamlan bíl.
I have an old car. Accusative 'bíl'.
❌ Regular dative singular for 'dagur': 'á þriðja dagi'
Incorrect — 'dagur' has the irregular i-umlaut dative singular 'degi', not 'dagi'.
✅ á þriðja degi
on the third day — dative singular 'degi'.
❌ Reading the plural off the nominative: pluralising every -ur word in -ar
Incorrect — only the -ar class does this; 'gestur' is -ir (gestir), and weak 'tími' is -ar but declines differently. The -ar default is a guess, not a guarantee.
✅ hestur → hestar, but gestur → gestir
Check the class; -ar is the safe default, not a universal rule.
Key Takeaways
- The -ar class is the largest strong masculine subclass: genitive singular -s, nominative plural -ar (hestur, hests, hestar).
- Singular endings -ur / – / -i / -s; plural -ar / -a / -um / -a. The accusative singular is the bare stem; the acc. and gen. plural coincide.
- The dative plural -um rounds a stem a to ö: dögum, höttum — never dagum, hattum.
- dagur is partly irregular: dative singular degi (i-umlaut) on top of dative plural dögum (u-umlaut).
- -ll and -nn stems double only in the nominative singular (bíll, steinn) and use the single-consonant stem everywhere else (bíl-, stein-). Whether the dative singular takes -i varies by word (steini but bíl).
- This is the productive default: an unknown -ur masculine is a safe bet to decline like hestur (tölvupóstur → tölvupóstar).
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Start learning Icelandic→Related Topics
- Strong Masculine Nouns: OverviewA2 — The strong masculine declensions — the largest noun group, marked by a genitive singular in -s and a nominative plural in -ar or -ir — with the all-important insight that the -ur of the nominative is an ending, not part of the stem.
- U-Umlaut as a Sound Alternation (a → ö)A2 — When a u appears (or once appeared) in the next syllable, a stem 'a' is rounded to 'ö' — barn → börn, dagur → dögum, kalla → köllum. This is the living u-umlaut (u-hljóðvarp), an automatic, predictable rounding that explains why so many Icelandic paradigms 'change their vowel'.