breyta ("to change / alter") is conjugated as a perfectly regular weak Class-2 verb — breyti, breytti, breytt — and yet it sits behind a remarkable number of learner errors, for one reason: its object is in the dative, not the accusative. You breytir áætluninni "change the plan," where áætluninni is dative. English gives no warning, since "change the plan" looks like an ordinary direct object. On top of that, breyta is strictly transitive: to say something changes on its own — the weather, your mood, the times — you must switch to the middle breytast. Get the dative and the transitive/intransitive split right and breyta is fully tamed. Orthography: the double tt is genuine (breytti, breytt), and the stem ey never u-umlauts (við breytum, never "breytöm").
Conjugation
Class: weak, Class 2 (the -ti preterite, doubling to -tti after the t-final stem breyt-). Auxiliary: hafa — ég hef breytt "I have changed." The ey diphthong blocks any u-umlaut, so við breytum keeps its vowel.
| Principal parts | |
|---|---|
| Infinitive | að breyta |
| 1sg present | breyti |
| 1sg past | breytti |
| 3pl past | breyttu |
| Supine | breytt |
| Person | Present (nútíð) | Past (þátíð) |
|---|---|---|
| ég | breyti | breytti |
| þú | breytir | breyttir |
| hann / hún / það | breytir | breytti |
| við | breytum | breyttum |
| þið | breytið | breyttuð |
| þeir / þær / þau | breyta | breyttu |
| Person | Present subjunctive | Past subjunctive |
|---|---|---|
| ég | breyti | breytti |
| þú | breytir | breyttir |
| hann / hún / það | breyti | breytti |
| við | breytum | breyttum |
| þið | breytið | breyttuð |
| þeir / þær / þau | breyti | breyttu |
| Non-finite & imperative | |
|---|---|
| Imperative (þú) | breyttu! |
| Imperative (þið) | breytið! |
| Supine | breytt |
| Past participle (m/f/n) | breyttur / breytt / breytt |
| Middle voice (miðmynd) | breytast — "to change (intransitively), become different" |
The dative object: breyta einhverju
breyta governs the dative, so the thing you change appears in the dative case: breyta áætluninni (the plan), breyta reglunum (the rules), breyta heiminum (the world). This is not random. A recurring pattern in Icelandic is that verbs of directing, managing or affecting something — acting on it rather than physically creating or consuming it — take the dative: stýra (steer), stjórna (control, govern), breyta (change, alter), hreyfa (move). The intuition is that you do not seize and transform the object outright (which would be the accusative of búa til, "make"); you nudge, manage or modify something that already exists. Thinking of breyta as "make a change to X" — where English itself uses "to" — makes the dative feel less alien. Still, there is no reliable way to predict the case from the English translation alone, so mark breyta in memory as a dative verb and decline accordingly.
Við þurfum að breyta áætluninni — flugið var fært fram.
We need to change the plan — the flight was moved up. — breyta + dative (áætluninni); the headline construction.
Hún breytti uppskriftinni aðeins og notaði spelt í staðinn fyrir hveiti.
She changed the recipe a bit and used spelt instead of wheat. — past breytti + dative (uppskriftinni).
Þú getur ekki breytt fortíðinni, en þú ræður framtíðinni.
You can't change the past, but you control the future. — breyta + dative (fortíðinni); a common, slightly proverbial line.
breytast — change on its own (intransitive)
When nothing external is doing the changing — the weather shifts, prices move, a person grows up — Icelandic uses the anticausative middle breytast. The thing that changes is now the subject (nominative), and there is no dative object. This is the -st form's classic job: it strips away the external agent of breyta and leaves a self-contained "become different." English is sloppy here in a way Icelandic refuses to be: the single English verb "change" is labile, covering both "I changed the plan" (transitive) and "the plan changed" (intransitive) with no formal difference. Icelandic forces the choice — breyta (someone changes something) vs. breytast (something changes) — and the -st is the visible marker that no agent is involved. This is the same anticausative -st you see in opna / opnast ("open"), loka / lokast ("close") and stækka pairs; recognising it as a system, rather than a quirk of one verb, lets you predict the intransitive form across the whole language.
Veðrið breyttist snögglega og það fór að snjóa.
The weather changed suddenly and it started to snow. — breytast (intransitive); veðrið is the subject, no object.
Allt hefur breyst síðan ég flutti héðan.
Everything has changed since I moved away. — middle supine 'breyst'; intransitive 'has changed'.
Hann hefur ekkert breyst — alveg sami gamli Jón.
He hasn't changed at all — exactly the same old Jón. — breytast for a person changing of their own accord.
breyta í + accusative — "turn into / change into"
To express transformation into something, breyta pairs with í + accusative: breyta vatni í vín "turn water into wine." The corresponding intransitive — something turning into something else by itself — is breytast í + accusative.
Verkfræðingarnir breyttu gamla pakkhúsinu í glæsilega íbúð.
The engineers turned the old warehouse into a stylish flat. — breyta + dative object (pakkhúsinu) + í + accusative goal (íbúð).
Larfan breytist í fiðrildi á nokkrum vikum.
The caterpillar turns into a butterfly over a few weeks. — breytast í + accusative; intransitive transformation.
Note the case interplay in the first example: the thing you change is dative (pakkhúsinu), but the result it becomes is accusative after í (íbúð).
Common Mistakes
❌ Við þurfum að breyta áætlunina.
Incorrect — breyta takes the DATIVE: 'áætluninni', not the accusative 'áætlunina'.
✅ Við þurfum að breyta áætluninni.
We need to change the plan.
The defining error. breyta governs the dative; an accusative object marks a learner instantly.
❌ Veðrið breytti í dag.
Incorrect — the weather changes by itself, so use the middle: 'veðrið breyttist'.
✅ Veðrið breyttist í dag.
The weather changed today.
For intransitive "change" (no external agent), use breytast. Active breyta always needs a dative object that someone is changing.
❌ Hún breytaði reglunum.
Incorrect — breyta is a -ti verb (with double tt): the past is 'breytti', not '-aði'.
✅ Hún breytti reglunum.
She changed the rules.
breyta is weak Class 2 with a -ti preterite; the t-final stem doubles it to breytti. Never the tala-style breytaði.
❌ Ég hef mikið breytt undanfarið.
Ambiguous/incorrect for 'I've changed a lot' — you mean it intransitively, so use the middle: 'ég hef mikið breyst'.
✅ Ég hef mikið breyst undanfarið.
I've changed a lot lately.
To say you yourself have changed, use the middle breyst. Active breytt would need an object — what have you changed?
Key Takeaways
- breyti / breytir / breytti / breytt — a regular weak Class-2 verb (-ti past, doubling to -tti); the ey stem blocks u-umlaut.
- The headline rule: breyta takes a DATIVE object — breyta áætluninni, reglunum, heiminum.
- breytast (middle) = "change" intransitively (weather, prices, a person) — the thing that changes becomes the subject, no object.
- breyta í
- accusative = "turn / change into"; the object stays dative while the result after í is accusative (breyta pakkhúsinu í íbúð).
- Auxiliary is hafa: ég hef breytt (transitive) / ég hef breyst (intransitive).
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