að as Complementiser vs að as Infinitive Marker | Icelandic Grammar

The little word að does two completely different grammatical jobs, and English uses two different words for them. As a complementiser, að means "that" and introduces a full finite clause: ég veit að hann kemur "I know that he's coming." As an infinitive marker, að means "to" and sits in front of a bare verb: það er gott að synda "it's good to swim." Same word, same spelling, two unrelated functions. Because English keeps "that" and "to" apart, English speakers usually parse Icelandic að correctly by translation — but they stumble when the two uses sit close together, and (the costly error) they insert að after modal verbs that actually take a bare infinitive. This page disentangles the two *að*s so you always know which clause type follows.

Complementiser að — "that," introducing a finite clause

When að means "that," it introduces a finite clause — a clause with its own subject and a tensed (conjugated) verb. This is the að that follows verbs of saying, thinking, knowing, hoping, and feeling: segja að "say that," vita að "know that," halda að "think that," vona að "hope that." Everything after að is a complete little sentence with a subject and a finite verb.

Ég veit að hann kemur á morgun.

I know that he's coming tomorrow. (að = 'that' + finite clause: subject hann, finite verb kemur)

Hún segir að það sé satt.

She says that it's true. (að + finite clause; the verb sé is subjunctive after a reporting verb)

Ég held að við séum að verða of sein.

I think we're going to be late. (halda að + finite clause; séum subjunctive)

Notice the second and third examples use the subjunctive (sé, séum) rather than the indicative. This is the deep reason the two að*s matter: a complementiser *að introduces a finite clause, and a finite clause can carry mood — so after reporting and thinking verbs the verb often goes subjunctive (sé not er, komi not kemur). The infinitive-marker að, by contrast, is followed by a moodless infinitive, so the subjunctive question never even arises. (For the mood choice itself, see verbs/subjunctive-reported-speech.)

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Complementiser að = "that" + a finite clause (its own subject and a tensed verb). Because the clause is finite, it can carry mood — so the verb may be subjunctive (sé, komi) after verbs of saying/thinking. That mood possibility is the practical payoff of knowing which að you're looking at.

Infinitive marker að — "to," before a verb stem

When að means "to," it is the infinitive marker: it sits directly in front of a verb in its base (infinitive) form, with no subject of its own. að synda "to swim," að borða "to eat," að fara "to go." This is the að you see in dictionary citation forms (verbs are listed as að synda, að lesa) and after countless triggers: adjectives (gott að synda "good to swim"), nouns (tími til að fara "time to go"), and verb-plus-preposition frames (vonast til að koma "hope to come," langa til að sjá "want to see").

Það er gott að synda í köldum sjó.

It's good to swim in cold sea. (að = 'to' + infinitive synda; no subject in the að-phrase)

Ég vonast til að koma á laugardaginn.

I'm hoping to come on Saturday. (vonast til að + infinitive koma)

Hún gleymdi að loka glugganum.

She forgot to close the window. (gleyma að + infinitive loka)

Það er kominn tími til að fara heim.

It's time to go home. (tími til að + infinitive fara)

The diagnostic is simple: after infinitive-að, the verb is in its bare base form and there is no new subject. After complementiser-að, there is a fresh subject and a conjugated verb.

The same word, both jobs in one sentence

Because the two að*s look identical, the cleanest way to feel the difference is to see them side by side. In the sentences below, the first *að is the complementiser "that" (finite clause follows) and the second is the infinitive marker "to" (bare verb follows).

Ég veit að það er erfitt að læra íslensku.

I know that it's hard to learn Icelandic. (1st að = 'that' + finite 'það er'; 2nd að = 'to' + infinitive læra)

Hún sagði að hún ætlaði að hætta að reykja.

She said that she intended to quit smoking. (1st að = 'that' + finite clause; then ætla að + infinitive, hætta að + infinitive — a chain of infinitive-að)

Read the second one carefully: sagði að (complementiser, "that") opens a finite clause, and inside it ætlaði *að hætta and hætta **að reykja are both infinitive-*að "to." One sentence, three *að*s, two different jobs.

Here is the error that actually costs you. A small set of modal verbs — geta "can," mega "may," vilja "want," eiga "ought," munu "will," skulu "shall," kunna "know how to" — take a bare infinitive with no að. English "I can swim" has no "to," and Icelandic agrees: ég get synt (literally "I can swum/swim"), not \ég get að synda. Inserting *að after a modal is ungrammatical. (Modal government is its own topic — see verbs/modals-overview — but the að fact belongs here.)

Ég get synt í heila klukkustund.

I can swim for a whole hour. (geta + BARE infinitive — no að)

Þú mátt fara núna.

You may go now. (mega + bare infinitive — no að)

Við viljum hjálpa þér.

We want to help you. (vilja + bare infinitive — no að, even though English has 'to')

Contrast these with the að-taking verbs above (vonast *til að koma, gleyma **að loka). There is no shortcut rule that predicts which verbs take bare infinitives and which take *að — the modals take bare, many other verbs take að, and you learn the membership of each group by exposure. But the modals are a closed, learnable set, so memorise them as the "no að" verbs.

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Modals — geta, mega, vilja, eiga, munu, skulu, kunna — take a bare infinitive with no að: ég get synt, þú mátt fara, við viljum hjálpa. Inserting að after a modal (*ég get að synda) is the single most common að error for English speakers, because English "want to / ought to" make you expect a "to."

Why English speakers must stay alert

English hands you two separate words — that for the finite complement, to for the infinitive — so you rarely confuse the functions. The Icelandic difficulty is the reverse: one word, að, does both, so you have to read what follows to know which clause type you are in. That matters because only the finite (complementiser) clause can host a subjunctive: if you mis-analyse an infinitive að as a complementiser, you might wrongly expect a conjugated, possibly subjunctive verb; if you mis-analyse a complementiser að as an infinitive marker, you might strip the subject and leave a bare verb. And on the production side, the "to" in English want to, ought to, can misleads you into adding að after Icelandic modals, where none belongs. Train two habits: after að, check whether a fresh subject + finite verb follows (complementiser) or a bare verb, no subject follows (infinitive); and memorise the modals as the verbs that take no að at all.

Common Mistakes

❌ Ég get að synda.

No að after a modal — geta takes a bare infinitive: ég get synt.

✅ Ég get synt.

I can swim. (geta + bare infinitive, no að)

The flagship error. English "can swim" has no "to" anyway, but the broader habit of putting "to" after modals (want *to, ought to*) leaks að into Icelandic. Modals take no að.

❌ Við viljum að hjálpa þér.

No að — vilja is a modal, so 'want to help' is viljum hjálpa, bare infinitive.

✅ Við viljum hjálpa þér.

We want to help you. (vilja + bare infinitive)

English "want to" is the strongest pull toward this mistake. vilja is a modal here; the infinitive is bare. (Compare langa til að "want to," which does take að — a different verb with different government.)

❌ Ég vonast koma á morgun.

Missing að — vonast til takes the infinitive marker: vonast til að koma.

✅ Ég vonast til að koma á morgun.

I'm hoping to come tomorrow. (vonast til að + infinitive — að required here)

The mirror error: dropping að where it is required. Non-modal verbs and verb-plus-preposition frames (vonast til að, langa til að, biðja um að) keep the infinitive marker. The skill is knowing which group a verb is in.

❌ Ég veit að koma á morgun. (meaning 'I know that he's coming')

Missing the finite clause — complementiser að needs a subject + tensed verb: að hann kemur.

✅ Ég veit að hann kemur á morgun.

I know that he's coming tomorrow. (complementiser að + finite clause)

After complementiser að ("that"), you need a full finite clause with its own subject. Leaving a bare infinitive collapses "that he's coming" into something ungrammatical.

❌ Hún segir að það vera satt.

Wrong verb form — the complement clause is finite, so the verb is conjugated (subjunctive sé), not the infinitive vera.

✅ Hún segir að það sé satt.

She says that it's true. (finite clause after að; sé = subjunctive of vera)

Because complementiser að opens a finite clause, the verb must be conjugated — and after a reporting verb it is often the subjunctive (sé, not the infinitive vera or even the indicative er).

Key Takeaways

One word að does two jobs: complementiser "that" (+ finite clause) and infinitive marker "to" (+ bare verb).
Complementiser að introduces a clause with its own subject and a tensed verb — and that verb can be subjunctive (sé, komi) after verbs of saying/thinking.
Infinitive-marker að sits before a bare base verb with no subject: gott að synda, vonast til að koma.
Modals (geta, mega, vilja, eiga, munu, skulu, kunna) take a bare infinitive with NO að — ég get synt, not \ég get að synda*. This is the top error.
The diagnostic after any að: fresh subject + finite verb → complementiser; bare verb, no subject → infinitive marker.

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