Most Swedish nouns fit one of the five regular declensions, and even the umlaut nouns of class 3 — hand → händer, bok → böcker — are regular in the sense that their vowel change is patterned. This page collects the genuine outliers: nouns whose plural you cannot derive from any class and must simply know. They fall into three families, each small and closed: a handful of suppletive native words (man → män), the archaic -on body-part plurals (öga → ögon), and the Latin and Greek loans that imported their original plurals (museum → museer). The reassuring news is that there is no productive rule to master here — it is a short vocabulary list. The trap is the opposite of fear: it is over-regularising these high-frequency words, saying mannar or museumer because the regular machinery is so ingrained.
Suppletive native irregulars
A few of the oldest words in the language change their stem vowel in ways that go beyond ordinary umlaut, or change shape in ways no class predicts. They are extremely frequent, so the irregularity is well worth the memorising. Here are the core members across all four forms:
| Indef. sing. | Def. sing. | Indef. plural | Def. plural | Meaning |
|---|---|---|---|---|
| en man | mannen | män | männen | man / men |
| en mus | musen | möss | mössen | mouse / mice |
| en gås | gåsen | gäss | gässen | goose / geese |
| en ko | kon | kor | korna | cow / cows |
| en tand | tanden | tänder | tänderna | tooth / teeth |
The first three are the famous ones. Man → män, mus → möss, gås → gäss all change vowel and form a plural with no audible regular ending (notice män is bare; möss and gäss double the consonant). These are exact cognates of the English irregulars man → men, mouse → mice, goose → geese — the same Germanic vowel-fronting, frozen in both languages. Ko → kor is gentler: it adds -r (a relic -or on a vowel-final stem) with no vowel change, so it almost looks regular but belongs to no productive class. Tand → tänder sits on the border — it umlauts like a class 3 noun — and is often listed with hand and natt.
Det stod två män och väntade utanför porten.
Two men stood waiting outside the gate. en man → män — bare vowel change, no ending.
Vi har fått möss i källaren igen.
We've got mice in the basement again. en mus → möss — vowel change plus doubled consonant.
Vilda gäss flyger söderut på hösten.
Wild geese fly south in the autumn. en gås → gäss.
Bonden har tjugo kor på gården.
The farmer has twenty cows on the farm. en ko → kor — adds -r, no vowel change.
The -on body-part plurals: an Old Norse fossil
Two of the most everyday nouns in the body vocabulary have a plural in -on that survives from Old Norse and is shared with Icelandic. They are neuter, and their forms are worth drilling because they appear constantly:
| Indef. sing. | Def. sing. | Indef. plural | Def. plural | Meaning |
|---|---|---|---|---|
| ett öga | ögat | ögon | ögonen | eye / eyes |
| ett öra | örat | öron | öronen | ear / ears |
Notice the whole paradigm is irregular, not just the plural. The definite singular drops the -a and adds -t directly: öga → ögat (not ögaet), öra → örat. The plural replaces the -a with -on: ögon, öron. And the definite plural adds -en to that: ögonen, öronen. The ö of the stem stays ö throughout. This -on ending is a closed museum piece — in everyday modern Swedish only these two words carry it, so do not generalise it. (Watch out for the false friend hjärta "heart": its plural is the regular class-4 hjärtan, with the ordinary vowel-final -n, not an -on relic.) Seeing it as an Old Norse fossil, the cousin of the same forms in Icelandic, is the right mental filing: it is history, not a pattern to extend.
Hon har stora bruna ögon.
She has big brown eyes. ett öga → ögon — the -a becomes -on.
Stäng öronen, det smäller nu!
Cover your ears, it's about to bang! ett öra → öron.
Tårarna rann från hans ögon.
Tears ran from his eyes. Definite plural ögonen would be 'the eyes'; here indefinite ögon after the preposition.
Latin and Greek loan plurals — and the honest caveat
A set of learned borrowings, mostly neuter, kept the plural of their source language. The most frequent is ett museum → museer, where the Latin -um drops and a Swedish-flavoured -er is added; its definite singular drops -um too (museet). Here are the ones you will actually meet:
| Indef. sing. | Def. sing. | Indef. plural | Def. plural | Meaning |
|---|---|---|---|---|
| ett museum | museet | museer | museerna | museum / museums |
| ett centrum | centrumet | centrum (or centra) | centrumen | centre / centres |
| ett faktum | faktumet | fakta (or faktum) | fakta(na) | fact / facts |
| en examen | examen | examina | examina(na) | exam / degree |
| en kollega | kollegan | kollegor | kollegorna | colleague / colleagues |
Two honest notes that courses tend to flatten. First, several of these plurals are optional, and the modern recommendation of the Swedish Academy is to prefer the Swedish-style form: centrum (or older centra), faktum (or older fakta), forum (rather than fora), spektrum (rather than spektra). So presenting centra as the only correct plural is out of date — två centrum is now perfectly standard and increasingly preferred. Second, en kollega → kollegor is not really irregular at all: it is a perfectly regular class 1 -a → -or noun (the older Latinate kolleger has now yielded first place to kollegor in the dictionaries). It is listed here only because learners often expect a Latin -ae and second-guess the regular form.
Stockholm har dussintals museer värda ett besök.
Stockholm has dozens of museums worth a visit. ett museum → museer (the -um drops).
Det öppnade två nya centrum i förorten.
Two new centres opened in the suburb. ett centrum → centrum — Swedish-style zero plural, now preferred over 'centra'.
Mina kollegor och jag tar lunch klockan tolv.
My colleagues and I have lunch at twelve. en kollega → kollegor — regular -a → -or, despite the Latin look.
Nouns with no singular or no plural
A small but useful category: some nouns lack a number partner entirely. Pluralia tantum (plural-only) words include pengar ("money", no everyday singular), föräldrar ("parents") and syskon ("siblings", which is zero-plural and used mostly in the plural sense). On the other side, mass nouns like mjölk ("milk"), information and kött ("meat") have no ordinary plural — to count them you reach for a measure word (två liter mjölk). These are not "irregular" so much as defective, but they trip learners who try to force a missing form.
Har du några pengar på dig?
Do you have any money on you? 'pengar' is plural-only — there's no everyday *peng singular.
Mina föräldrar bor kvar i samma hus.
My parents still live in the same house. 'föräldrar' is normally used only in the plural.
Common Mistakes
❌ en man → mannar / manar
Incorrect — over-regularising. The plural is the suppletive 'män'.
✅ en man → män
a man → men — vowel change, no regular ending.
❌ ett museum → museumer / museums
Incorrect — the -um drops and you add -er: museer. Never the English -s.
✅ ett museum → museer
a museum → museums.
❌ ett öga → ögor / ögar
Incorrect — the irregular plural is 'ögon' (the -a becomes -on).
✅ ett öga → ögon
an eye → eyes — Old Norse -on plural.
❌ Insisting on 'centra' as the only plural of centrum
Incorrect — 'centra' is the older Latin form; modern Swedish prefers 'centrum' (zero plural).
✅ två centrum (eller centra)
two centres — the Swedish-style plural is now standard and preferred.
❌ en pengar → 'a money'
Incorrect — 'pengar' has no everyday singular; for one coin you'd say 'ett mynt'.
✅ pengar
money — a plural-only noun.
Key Takeaways
- These plurals can't be derived from the five classes — they are short closed lists to memorise, and the real risk is over-regularising (mannar, museumer).
- Suppletive natives: man → män, mus → möss, gås → gäss, ko → kor, tand → tänder — direct cognates of English men, mice, geese.
- The -on body-part plurals öga → ögon, öra → öron are an Old Norse fossil shared with Icelandic; the whole paradigm is irregular (ögat, ögon, ögonen).
- Latin/Greek loans: museum → museer is fixed, but many (centrum, faktum, forum) now prefer the Swedish-style plural — två centrum over centra. kollega → kollegor is actually regular.
- Some nouns are plural-only (pengar, föräldrar) or have no plural (mjölk, information) — count the latter with a measure word.
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Start learning Swedish→Related Topics
- Plural Class 3: -er and Umlaut PluralsB1 — The third Swedish plural declension: the indefinite plural in -er, covering many one-syllable en-words (sak → saker), stress-final loanwords (station → stationer, parti → partier), and a small closed set of umlaut nouns whose stem vowel changes (hand → händer, bok → böcker, fot → fötter). Definite plural -erna. The umlaut subgroup is not a productive rule but a memorisable handful of high-frequency words.
- The Five Plural DeclensionsA2 — Swedish builds plurals through five declension classes — -or, -ar, -er, -n, and a zero ending — not the English -s. This overview names all five, gives a model noun for each, and lays out the prediction rules competitors omit: gender plus the word's final sound forecasts the class about 80% of the time, so the system is far less random than it first looks.
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