opna (to open) | Icelandic Grammar

opna ("to open") is a model weak Class-1 verb — the same -aði machinery as tala — but it earns its own page for two reasons. First, it takes the accusative (opna hurðina "open the door"), which makes a deliberate contrast with its opposite loka "to close," which takes the dative. Second, opna is the perfect verb for learning the difference between an active action (ég opna "I open something") and the middle voice opnast (hurðin opnast "the door opens on its own"). Learn this pair and you understand one of the cleanest patterns in the language.

Conjugation

Class: weak, Class 1 (the -aði preterite). Auxiliary: hafa — ég hef opnað "I have opened."

Principal parts
Infinitive	að opna
3sg present	opnar
3sg past	opnaði
Supine	opnað

Person	Present (nútíð)	Past (þátíð)
ég	opna	opnaði
þú	opnar	opnaðir
hann / hún / það	opnar	opnaði
við	opnum	opnuðum
þið	opnið	opnuðuð
þeir / þær / þau	opna	opnuðu

Person	Present subjunctive	Past subjunctive
ég	opni	opnaði
þú	opnir	opnaðir
hann / hún / það	opni	opnaði
við	opnum	opnuðum
þið	opnið	opnuðuð
þeir / þær / þau	opni	opnuðu

Non-finite & imperative
Imperative (þú)	opnaðu
Imperative (þið)	opnið!
Supine	opnað
Past participle (m/f/n)	opnaður / opnuð / opnað
Middle voice (miðmynd)	opnast — "to open (by itself), to come open"

The u-umlaut that doesn't happen

Here is the point that trips up learners who have just mastered tala → tölum. The u-umlaut rule (a → ö before a -u- ending) only applies to the vowel a. The stem vowel of opna is o, not a — and o never umlauts. So "we open" is opnum, never öpnum, and the past plural is opnuðum / opnuðu, never öpnuðum.

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U-umlaut targets short a only. If a verb's stem vowel is o, i, e, u or anything else, the -um and -uðu endings attach with no vowel change. opna → opnum, loka → lokum, vona → vonum. Don't let the "we"-form reflex you learned from tala bleed onto o-stems.

opna + accusative — "open something"

The transitive opna takes a plain accusative object: opna hurðina (the door), opna gluggann (the window), opna pakkann (the parcel). There is no preposition.

Geturðu opnað gluggann? Það er heitt hérna inni.

Can you open the window? It's hot in here.

Búðin opnar klukkan tíu á morgnana.

The shop opens at ten in the mornings.

Ég opnaði tölvupóstinn en svaraði honum ekki strax.

I opened the email but didn't reply to it right away.

Note that in búðin opnar ("the shop opens") the verb is used intransitively with the shop as a normal nominative subject — Icelandic, like English, lets a business "open" without the middle voice.

opnast — "open by itself" (the anticausative middle)

When a thing comes open with no one opening it — a door swings open, a flower opens, a wound reopens — Icelandic uses the middle voice opnast. The thing that opens is now the subject, and there is no agent.

Hurðin opnaðist hægt og marraði.

The door opened slowly and creaked.

Glugginn opnast ekki, hann er fastur.

The window won't open, it's stuck.

Compare the active and middle directly: ég opna hurðina = I open the door (I am the agent); hurðin opnast = the door opens (it happens to it, by itself). English collapses both into "open"; Icelandic keeps the agent-vs-spontaneous distinction visible in the -st ending. The past of opnast is opnaðist (note the -ð- of the past plus the -st).

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This active/middle pair is the most reliable way to internalise the Icelandic middle voice. Whenever English would let a verb be both "X opens Y" and "Y opens" with the same word, Icelandic usually splits them: the transitive stays bare (opna) and the intransitive "by itself" reading takes -st (opnast). The same logic gives you loka / lokast and breyta / breytast — learn the habit here and it generalises.

Figurative uses: an account, your eyes, a discussion

opna is not only physical. You open a bank account, an email, a discussion, or your eyes — all with the same verb and the accusative.

Ég ætla að opna reikning í þessum banka.

I'm going to open an account at this bank.

Hún opnaði augun og sá að klukkan var orðin tíu.

She opened her eyes and saw it was already ten o'clock.

Common Mistakes

❌ Við öpnum búðina klukkan níu.

Incorrect — the stem vowel is o, which never takes u-umlaut; it stays opnum

✅ Við opnum búðina klukkan níu.

We open the shop at nine.

❌ Opnaðu hurðinni.

Incorrect — opna takes the accusative (hurðina), unlike its opposite loka which takes the dative

✅ Opnaðu hurðina.

Open the door.

❌ Hurðin opnaði af sjálfu sér.

Incorrect — a thing opening by itself needs the middle voice opnast, not the active opnaði

✅ Hurðin opnaðist af sjálfu sér.

The door opened by itself.

❌ Ég opndi pakkann.

Incorrect — opna is an -aði verb, not a -di verb; the past is opnaði

✅ Ég opnaði pakkann.

I opened the parcel.

Key Takeaways

opna / opnar / opnaði / opnað — a regular weak Class-1 verb (-aði past).
No u-umlaut: the stem vowel is o, so "we open" is opnum (not öpnum) and the past plural is opnuðum / opnuðu.
Transitive opna takes the accusative (opna hurðina) — the mirror image of loka
- dative.
The middle voice opnast means "to open by itself" (hurðin opnast), with the thing as subject and no agent.
Imperative opnaðu; auxiliary hafa (ég hef opnað).

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