In English an adjective is a fixed word: old is old whether the thing is one or many, the subject or the object, a man or a window. The Icelandic adjective is the opposite — it is one of the most heavily inflected words in the language. It does two things English adjectives never do. First, it agrees with its noun in three dimensions at once: gender, number, and case. Second, it has two entire declensions — a strong one and a weak one — and which you use depends not on the adjective's meaning but on whether the noun phrase is definite or indefinite. This page is the map. It shows you the system so the detailed paradigm pages (linked at the bottom) make sense; here we establish why a single adjective like gamall ("old") can appear as gamall, gömul, gamalt, gamli, gamla and more.
Agreement: gender × number × case
Every time you use an adjective, it must match its noun on three axes:
- Gender — masculine (kk), feminine (kvk), or neuter (hk)
- Number — singular or plural
- Case — nominative, accusative, dative, genitive
Watch gamall change with the gender of the noun, all in the nominative singular, all indefinite:
| Noun | Gender | Adjective + noun |
|---|---|---|
| maður ("man") | masculine | gamall maður |
| kona ("woman") | feminine | gömul kona |
| hús ("house") | neuter | gamalt hús |
Þarna býr gamall maður með stóran hund.
An old man lives there with a big dog. Masculine 'gamall' agrees with 'maður'.
Það kom gömul kona inn í búðina.
An old woman came into the shop. Feminine 'gömul' — note the u-umlaut: gamall → gömul.
Þau keyptu gamalt hús úti á landi.
They bought an old house out in the countryside. Neuter 'gamalt' — the neuter strong ending is -t.
Three points of spelling to fix immediately. The neuter strong ending is -t (gamalt). The feminine strong nominative singular shows the u-umlaut — gamall rounds its stem a to ö, giving gömul (the ending carries a hidden u that triggers the rounding, exactly the rule from u-umlaut in plurals). And the masculine gamall keeps its double -ll.
Strong vs weak: the definiteness switch
Here is the feature that has no English parallel at all. The same adjective has two complete sets of endings, and you choose between them based on the definiteness of the noun phrase:
- Strong declension — used when the noun is indefinite ("an old man," "old houses").
- Weak declension — used when the noun is definite: after the suffixed article, after a demonstrative (þessi "this", sá "that"), or after a possessive (minn "my").
Compare the strong and weak forms of gamall, nominative singular, in all three genders:
| Gender | Strong (indefinite) | Weak (definite) |
|---|---|---|
| Masculine | gamall maður ("an old man") | gamli maðurinn ("the old man") |
| Feminine | gömul kona ("an old woman") | gamla konan ("the old woman") |
| Neuter | gamalt hús ("an old house") | gamla húsið ("the old house") |
Look at the difference. The strong forms are varied and consonant-heavy (gamall, gömul, gamalt); the weak forms are gentle and vowel-final (gamli, gamla, gamla). The weak forms all end in -i or -a, which is why the weak declension is sometimes called the "-a/-i declension." Crucially, the weak feminine and neuter are identical (gamla), so the weak set collapses three genders into two shapes in the nominative singular.
Gamall maður settist hjá mér í strætó.
An old man sat down next to me on the bus. Indefinite → STRONG 'gamall'.
Gamli maðurinn á horninu gefur dúfunum brauð.
The old man on the corner feeds the pigeons bread. Definite (article on 'maðurinn') → WEAK 'gamli'.
Ég sá gömul hjón ganga niður götuna.
I saw an old couple walking down the street. Indefinite plural → STRONG 'gömul'.
Þessi gamla kona man tímana tvenna.
This old woman remembers the old days. After the demonstrative 'þessi' → WEAK 'gamla', even though there's no article suffix.
That last example is the key insight, and it is one that most references bury: the strong/weak choice is about the whole noun phrase's definiteness, not the adjective itself. The adjective gamla is weak in þessi gamla kona because þessi ("this") makes the phrase definite — there is no article on kona at all. Add "the," "this," "that," or "my," and the same adjective flips from strong to weak. The adjective is just reading the definiteness of the phrase it sits in.
Predicate adjectives are strong
When the adjective comes after the verb "to be" (or "seem," "become") and describes the subject — a predicate adjective — it uses the strong form, agreeing with the subject in gender and number. It does not go weak even when the subject is definite, because the adjective is not sitting inside the definite noun phrase; it's standing apart in the predicate.
Maðurinn er gamall.
The man is old. Predicate position → STRONG 'gamall', even though 'maðurinn' is definite. The adjective isn't inside the noun phrase.
Konan var orðin gömul og þreytt.
The woman had grown old and tired. Predicate 'gömul' (feminine strong) and 'þreytt' (feminine strong) after 'vera/verða'.
Húsið er gamalt en vel við haldið.
The house is old but well maintained. Predicate neuter strong 'gamalt'.
So the rule of thumb sharpens: weak only when the adjective is attributive (sitting before the noun) inside a definite phrase. Predicate adjectives are always strong.
Comparison: a quick orientation
Adjectives also form a comparative ("older") and superlative ("oldest"). The regular pattern adds -ari (comparative) and -astur (superlative): ríkur "rich" → ríkari → ríkastur. Many high-frequency adjectives, including gamall, are irregular: gamall → eldri → elstur ("old → older → oldest"). The comparative form (eldri) is itself always weak in declension; the superlative (elstur) declines strong or weak like a normal adjective. The full mechanics belong on the comparison pages — here, just register that comparison is a third layer on top of the gender/number/case agreement and the strong/weak split.
Bróðir minn er eldri en ég, en pabbi er elstur.
My brother is older than me, but Dad is the oldest. Irregular comparison: gamall → eldri → elstur.
Common Mistakes
❌ Þetta er gamall hús.
Incorrect — 'hús' is neuter, so the adjective must agree: neuter strong is gamalt.
✅ Þetta er gamalt hús.
This is an old house. Neuter strong ending -t.
❌ Gamall maðurinn gengur hægt.
Incorrect — 'maðurinn' is definite (has the article), so the adjective must be weak.
✅ Gamli maðurinn gengur hægt.
The old man walks slowly. Definite phrase → weak 'gamli'.
❌ Ég hitti gamall vin í gær.
Incorrect — leaving the adjective in its dictionary form; the accusative masculine strong of gamall is 'gamlan'.
✅ Ég hitti gamlan vin í gær.
I met an old friend yesterday. The adjective inflects for case too — accusative 'gamlan'.
❌ Þessi gömul kona er nágranni minn.
Incorrect — after the demonstrative 'þessi' the phrase is definite, so the adjective goes weak: gamla.
✅ Þessi gamla kona er nágranni minn.
This old woman is my neighbour. Demonstrative makes it definite → weak 'gamla'.
❌ Maðurinn er gamli.
Incorrect — a predicate adjective is strong, not weak, even with a definite subject.
✅ Maðurinn er gamall.
The man is old. Predicate position → strong 'gamall'.
Key Takeaways
- The Icelandic adjective agrees with its noun in gender, number, and case — English has no agreement at all.
- It has two full declensions: strong (indefinite, gamall maður) and weak (definite, gamli maðurinn).
- The choice is set by the definiteness of the whole noun phrase: an article, a demonstrative (þessi/sá), or a possessive (minn) triggers the weak form — the same adjective flips when you add "the."
- Strong nom.sg. of gamall: gamall / gömul / gamalt (neuter -t, feminine u-umlaut). Weak: gamli / gamla / gamla (all in -i/-a).
- Predicate adjectives (after vera/verða) are always strong: maðurinn er gamall.
- Comparison (gamall → eldri → elstur) is a further layer on top; comparatives always decline weak.
Now practice Icelandic
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Icelandic→Related Topics
- The Strong (Indefinite) DeclensionA2 — The full strong adjective paradigm — used when the noun phrase is indefinite and for predicate adjectives — laid out for fallegur across all genders, cases, and numbers, with the neuter -t, the consonant-heavy feminine and genitive endings, and the u-umlaut that surfaces in a-stem adjectives like svangur → svöng.
- The Weak (Definite) DeclensionA2 — The full weak adjective paradigm — used after the definite article, demonstratives, and possessives — laid out for gamall, with its tiny inventory of -i and -a (and -u) endings, the rule that definiteness drives the choice, and the redundant double-marking (gamli maðurinn) that English speakers systematically under-produce.