Reciprocal and Anticausative -st | Icelandic Grammar

The Icelandic middle voice — the verb form built by suffixing -st — does several jobs, but two of them are by far the most productive, meaning a speaker can apply them to fresh verbs and be understood. The first is the reciprocal: with a plural subject, -st means the people do the action to one another (þau hittust "they met each other"). The second is the anticausative: -st takes a transitive verb and removes its agent, so the event simply happens by itself (hurðin opnaðist "the door opened"). Both are regular enough that you can usually predict the meaning — which sets them apart from the lexicalised -st verbs like finnast "seem" or komast "manage to get," whose meanings you have to learn one by one. This page covers the reciprocal and the anticausative, how each transforms the base verb, and why English speakers reach for the wrong construction. (The lexicalised experiencer -st, like finnast, has its own page and is deliberately left out here.)

The reciprocal -st: 'each other', folded into the verb

English marks reciprocity with a separate phrase — each other, one another. Icelandic folds it straight into the verb with -st. So where English needs three words ("they met each other"), Icelandic needs one inflected verb: þau hittust. The construction is inherently plural-subject: there must be at least two participants for "each other" to mean anything, so the reciprocal -st only makes sense with við, þið, þeir, þær, þau or a plural noun.

The most common reciprocal -st verbs are everyday social ones:

Base verb	Reciprocal -st	Meaning
hitta "meet (s.o.)"	hittast	meet (each other), meet up
sjá "see"	sjást	see each other
kyssa "kiss (s.o.)"	kyssast	kiss (each other)
tala við "talk to"	talast við	be on speaking terms, talk to each other
berja "hit (s.o.)"	berjast	fight (each other)
heyra "hear"	heyrast (við)	be in touch, hear from each other

The key insight is that the reciprocal -st replaces the English "each other." Because the reciprocity already lives in the verb, you do not add the Icelandic phrase for "each other" (hvort annað, hvert annað) on top — that would be saying it twice.

Vinirnir hittust á kaffihúsi og spjölluðu fram á kvöld.

The friends met up at a café and chatted into the evening. (hittast — reciprocal 'meet each other')

Þau kysstust í fyrsta sinn á gamlárskvöld.

They kissed for the first time on New Year's Eve. (kyssast — reciprocal)

Strákarnir börðust á skólalóðinni og voru sendir til skólastjórans.

The boys fought on the playground and were sent to the principal. (berjast — 'fight each other')

Við höfum ekki talast við síðan í fyrra.

We haven't been on speaking terms / talked to each other since last year. (talast við — reciprocal)

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The reciprocal -st is "each other" built into the verb. So þau sjást already means "they see each other" — adding hvort annað is redundant. This is the everyday source of the goodbye við sjáumst! ("see you!" = "we'll see each other").

Some of these have a second, non-reciprocal life too — sjást also means "be visible," heyrast also means "be audible" — but with a human plural subject the reciprocal reading is the default. Context, especially the subject, sorts them out.

The anticausative -st: the event happens by itself

The anticausative is the other productive job, and it works on a completely different principle: it detransitivises the verb. Start with a transitive verb that has an agent and an object — ég opna dyrnar "I open the door." The agent (ég) makes something happen to the object (dyrnar). Add -st and the agent disappears: the former object becomes the subject, and the event is presented as happening on its own, with no one doing it — dyrnar opnast "the door opens." This is exactly the alternation English shows in a small set of verbs ("I open the door" / "the door opens", "I broke the glass" / "the glass broke"), except that English does it with a bare verb and Icelandic marks it overtly with -st.

Transitive (with agent)	Anticausative -st (no agent)
ég opna dyrnar — I open the door	dyrnar opnast — the door opens
ég loka glugganum — I close the window	glugginn lokast — the window closes
hann breytir áætluninni — he changes the plan	áætlunin breytist — the plan changes
þau stækka húsið — they enlarge the house	húsið stækkar — the house grows

The pair to study closely is breyta / breytast. With breyta there is someone doing the changing, and the thing changed is in the dative (breyta áætluninni "change the plan"). With breytast there is no changer: the subject changes of its own accord.

Hann breytti áætluninni á síðustu stundu.

He changed the plan at the last minute. (transitive breyta + dative — there is an agent)

Áætlunin breyttist á síðustu stundu.

The plan changed at the last minute. (anticausative breytast — no agent, it just changed)

Hurðin opnaðist hægt af sjálfu sér.

The door opened slowly by itself. (anticausative opnast, past opnaðist)

Búðin lokast klukkan sex, svo við verðum að flýta okkur.

The shop closes at six, so we have to hurry. (anticausative lokast — the shop closes, no one named)

Why the anticausative matters: Icelandic's 'no-agent' event

Here is the deep point that makes this page worth its space. English mostly uses the passive to background an agent ("the door was opened," "the plan was changed") — but the passive still implies a doer, even an unnamed one. When you genuinely want to say an event happened with no agent at all — spontaneously, by itself — Icelandic prefers the anticausative -st, not the passive. Hurðin opnaðist is "the door opened" with the strong sense that nobody opened it; hurðin var opnuð is "the door was opened" and invites the question "by whom?". The -st form is Icelandic's main grammatical tool for the agent-less, spontaneous event.

This is precisely the role played by se / si in Romance (Spanish la puerta se abrió, Italian la porta si è aperta) and by sich in German (die Tür öffnete sich). If you know any of those languages, map the Icelandic -st onto them directly: it is the same "self/spontaneous" middle, descended from the same kind of reflexive pronoun. English is the odd one out here, having lost a dedicated marker and pressing either a bare intransitive ("the door opens") or the passive into service.

Veðrið er að breytast — það er að hvessa.

The weather is changing — the wind is picking up. (anticausative; no one changes the weather)

Glerið brotnaði þegar það datt á gólfið.

The glass broke when it fell on the floor. (anticausative brotna(st)-type — it broke by itself)

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Decision rule: if there is a doer, even an unnamed one, use the periphrastic passive (vera + participle: dyrnar voru opnaðar "the doors were opened"). If the event happens by itself, use the anticausative -st (dyrnar opnuðust "the doors opened"). The contrast is real and Icelandic speakers feel it.

Form note: -st attaches to the inflected verb

Mechanically, both readings build their forms the same way: -st attaches to the inflected verb, at the very end. So you conjugate the verb first, then add -st (with the predictable collisions covered on the Middle Voice Forms page). For the anticausative this gives a full tense paradigm: present opnast, past opnaðist, supine opnast (perfect hefur opnast). For the reciprocal, remember the subject is always plural, so you mostly meet the plural forms: hittumst / hittust, sjáumst / sáumst.

Dyrnar að safninu opnast klukkan tíu og lokast klukkan fimm.

The museum doors open at ten and close at five. (anticausative present — opnast, lokast)

Við hittumst loksins eftir margra ára bréfaskriftir.

We finally met after years of writing to each other. (reciprocal past hittumst)

Common Mistakes

❌ Þau hittust hvort annað í gær.

Incorrect — the reciprocal -st already means 'each other'; adding 'hvort annað' is redundant.

✅ Þau hittust í gær.

They met (each other) yesterday.

❌ Hurðin opnar þegar maður ýtir á takkann.

Incorrect — without an agent the verb must be anticausative -st: the door opens by itself, hurðin opnast.

✅ Hurðin opnast þegar maður ýtir á takkann.

The door opens when you press the button.

❌ Áætlunin var breytt af sjálfu sér.

Incorrect — for a spontaneous, agent-less change use the anticausative, not the passive: áætlunin breyttist.

✅ Áætlunin breyttist.

The plan changed (by itself).

❌ Við berjumst hvor við annan.

Incorrect — berjast already means 'fight each other'; the reciprocal is in the -st, so drop the extra phrase.

✅ Við berjumst.

We're fighting (each other).

❌ Glugginn lokaði af vindinum.

Incorrect — 'the window closed' (event, no agent) is the anticausative lokast: glugginn lokaðist. (lokar would need a subject doing the closing.)

✅ Glugginn lokaðist af vindinum.

The window closed because of the wind.

Key Takeaways

The two productive -st jobs are the reciprocal ("each other") and the anticausative ("by itself").
Reciprocal -st folds English "each other" into the verb and needs a plural subject: hittast, sjást, kyssast, talast við, berjast. Never add hvort annað — it is already in the verb. (Source of the goodbye við sjáumst!)
Anticausative -st detransitivises: it removes the agent so the event happens on its own — ég opna dyrnar → dyrnar opnast; hann breytir áætluninni → áætlunin breytist.
The anticausative is Icelandic's natural way to say "X happens with no agent," parallel to Romance se/si and German sich — and it is not the passive: a passive (vera
- participle) still implies a doer.
-st attaches to the inflected verb (opnast, opnaðist); reciprocals are inherently plural-subject.

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