opna ("to open") and loka ("to close") are a natural pair, and both are tidy weak class-1 verbs with no vowel changes. But they hide a famous Icelandic trap: opposite meanings, opposite cases. You open something in the accusative — opna hurðina — but you close something in the dative — loka hurðinni. Nothing about the meaning predicts this; it is a fact about each verb you simply have to lock in. Learn the two together so the contrast sticks.
Conjugation
Both are weak, class 1 (the -aði class). Stems opn- and lok-; past marker -aði; supine -að.
| Principal parts | ||
|---|---|---|
| opna (open) | loka (close) | |
| Infinitive | að opna | að loka |
| 3sg present | opnar | lokar |
| 3sg past | opnaði | lokaði |
| Supine | opnað | lokað |
| Person | opna — present | opna — past | loka — present | loka — past |
|---|---|---|---|---|
| ég | opna | opnaði | loka | lokaði |
| þú | opnar | opnaðir | lokar | lokaðir |
| hann / hún / það | opnar | opnaði | lokar | lokaði |
| við | opnum | opnuðum | lokum | lokuðum |
| þið | opnið | opnuðuð | lokið | lokuðuð |
| þeir / þær / þau | opna | opnuðu | loka | lokuðu |
| Person | opna — pres. subj. | opna — past subj. | loka — pres. subj. | loka — past subj. |
|---|---|---|---|---|
| ég | opni | opnaði | loki | lokaði |
| þú | opnir | opnaðir | lokir | lokaðir |
| hann / hún / það | opni | opnaði | loki | lokaði |
| við | opnum | opnuðum | lokum | lokuðum |
| þið | opnið | opnuðuð | lokið | lokuðuð |
| þeir / þær / þau | opni | opnuðu | loki | lokuðu |
| Non-finite & imperative | ||
|---|---|---|
| Imperative (þú) | opnaðu | lokaðu |
| Imperative (þið) | opnið | lokið |
| Past participle (m/f/n) | opnaður / opnuð / opnað | lokaður / lokuð / lokað |
| Middle voice (miðmynd) | opnast — "open by itself" | lokast — "close by itself" |
The case asymmetry — the whole point of this page
This is the single most important thing on the page:
| Verb | Case of object | Example |
|---|---|---|
| opna | accusative | opna hurðina (open the door) |
| loka | dative | loka hurðinni (close the door) |
Same noun (hurð "door"), but opna puts it in the accusative (hurðina) and loka puts it in the dative (hurðinni). The same holds for gluggi (window): opna gluggann (acc.) vs loka glugganum (dat.); and for dyr (a doorway, plural): opna dyrnar (acc.) vs loka dyrunum (dat.).
Geturðu opnað gluggann? Það er svo heitt hérna.
Can you open the window? It's so hot in here.
Mundu að loka glugganum þegar þú ferð.
Remember to close the window when you leave.
Hún opnaði dyrnar og hleypti köttinum inn.
She opened the door and let the cat in.
Lokaðu hurðinni, það er dragsúgur.
Close the door, there's a draught.
Opið and Lokað — the signs on every door
You will read these two words long before you conjugate the verbs. Opið ("open") and Lokað ("closed") are the neuter participle forms used as shop signs. They are neuter because they describe það — the unstated "it" (the place). On a sign they stand alone; in a sentence they pair with er: Búðin er opin "the shop is open" (feminine opin, agreeing with búð).
Það stendur „Lokað
It says 'Closed' on the door — we're too late.
Bakaríið er opið til klukkan sex.
The bakery is open until six o'clock.
opnast / lokast — opening and closing by themselves
The middle voice turns the action intransitive: opnast = "to open (by itself, come open)" and lokast = "to close (by itself, shut)." Use these when nobody is doing the action to a thing — the door just opens or shuts.
Hurðin opnast sjálfkrafa þegar þú gengur að henni.
The door opens automatically when you walk up to it.
Búðin lokar klukkan sjö á virkum dögum.
The shop closes at seven on weekdays.
Common Mistakes
❌ Lokaðu hurðina.
loka takes the dative — hurðina is accusative
✅ Lokaðu hurðinni.
Close the door.
❌ Opnaðu glugganum.
opna takes the accusative — glugganum is dative
✅ Opnaðu gluggann.
Open the window.
❌ Búðin er lokað.
As a predicate adjective it must agree: búð is feminine → lokuð
✅ Búðin er lokuð.
The shop is closed.
❌ Hvenær opnar búðin sig?
No reflexive sig here — use plain opnar, or the middle voice opnast for 'opens by itself'
✅ Hvenær opnar búðin?
When does the shop open?
Key Takeaways
- opna / opnaði / opnað and loka / lokaði / lokað — two regular weak class-1 verbs.
- The asymmetry: opna + ACCUSATIVE (opna hurðina) but loka + DATIVE (loka hurðinni).
- Opið / Lokað are the neuter sign forms; in a sentence the participle agrees: búðin er opin / lokuð.
- opnast / lokast (middle voice) = open / close by itself.
- Imperatives fuse the pronoun: opnaðu / lokaðu.
Now practice Icelandic
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Start learning Icelandic→Related Topics
- opna (to open)A2 — Full conjugation of the weak Class-1 verb opna (opna / opnaði / opnað), which takes an ACCUSATIVE object (opna hurðina), the anticausative middle opnast ('open by itself'), and why its o-stem does NOT take the u-umlaut (opnum, not öpnum).
- loka (to close)A2 — Full conjugation of the weak Class-1 verb loka (loka / lokaði / lokað), which surprisingly takes a DATIVE object (loka hurðinni, loka glugganum), the anticausative middle lokast ('close by itself'), the adjective lokaður ('closed'), and why its o-stem takes NO u-umlaut (lokum, not lökum).
- Annotated Text: Public Notices and SignsA2 — A set of authentic-style Icelandic signs and notices — fully glossed, then unpacked for the sign register: the bare neuter past participle as an impersonal predicate (Opið, Lokað, Bannað), the prohibition frame bannað að + infinitive, the agreeing passive participle (Reykingar bannaðar), and vinsamlegast + the 2pl imperative (Vinsamlegast slökkvið …).