Icelandic verbs split into two great families. Weak verbs build their past tense by adding a dental ending — -aði, -di, -ti — to a fixed stem (tala → talaði, "spoke"), the way English adds -ed. Strong verbs do something English has mostly forgotten how to do: they form the past by changing the stem vowel itself, with no added ending. This vowel change is called ablaut (Icelandic hljóðskipti), and it's the same machinery behind English sing–sang–sung and give–gave–given — relics of a system that Old Norse, and modern Icelandic, kept fully alive. This page introduces the strong verbs as a class: how ablaut works, why a strong verb has four principal parts rather than one or two, and the single feature English speakers most reliably miss — that the past singular and past plural can have different vowels. The seven detailed classes have their own pages; the present-tense vowel change has its own page too. Here, your job is to recognise a strong verb and learn to cite all four of its parts.
Ablaut: the past lives in the vowel
A weak verb keeps one stem and bolts a past ending onto it. A strong verb has no past ending at all — the past is signalled purely by swapping the vowel:
| Infinitive | Past (he _) | How the past is built | |
|---|---|---|---|
| Weak | tala ("speak") | hann talaði | stem + ending -aði |
| Strong | taka ("take") | hann tók | vowel change a → ó, no ending |
Hann talaði adds a syllable; hann tók adds nothing — it just re-vowels tak- to tók. This is why you can't predict a strong verb's past from its infinitive the way you can a weak one's. You have to learn the vowels, and there is more than one of them to learn.
Hann tók strætó í vinnuna í morgun.
He took the bus to work this morning. Strong past 'tók' — vowel change from 'taka', no -ð-/-að- ending.
Ég talaði við lækninn í gær.
I spoke to the doctor yesterday. Weak past 'talaði' — contrast: the ending '-aði' is added, no vowel change.
Four principal parts — and why you need all four
A weak verb is essentially predictable from its infinitive. A strong verb is not — its vowels shift in ways that vary by verb and by class — so the dictionaries cite four principal parts, and learning a strong verb means learning all four:
- Infinitive (nafnháttur) — the dictionary form: taka.
- Preterite singular (þátíð eintala), cited as the 1st/3rd person: tók ("I/he took").
- Preterite plural (þátíð fleirtala), cited as the 3rd person: tóku ("they took").
- Supine (sagnbót) — the form used with hafa to build the perfect: tekið ("(have) taken").
The convention is to list them in that order, separated by commas: taka – tók – tóku – tekið. Here are three high-frequency verbs cited in full:
| Infinitive | Pret. sg (ég / hann) | Pret. pl (þeir) | Supine (hef _) | Meaning |
|---|---|---|---|---|
| taka | tók | tóku | tekið | take |
| koma | kom | komu | komið | come |
| finna | fann | fundu | fundið | find |
Track finna across its row and you see why one or two forms aren't enough: finna → fann → fundu → fundið runs through three different vowels (i / a / u). Knowing only "finna means find, past is fann" leaves you unable to say "they found" (fundu) or "I have found" (ég hef fundið). The four parts aren't pedantry — each one feeds a different chunk of the tense system.
Ég hef aldrei komið til Akureyrar.
I've never been (come) to Akureyri. The supine 'komið' builds the perfect with 'hef'.
The split English forgot: past singular vs past plural
Now the deepest point, and the one competitors bury. In many strong verbs the preterite singular and the preterite plural carry different vowels. English merged these centuries ago — modern English uses one past form for all persons (I found, they found) — but Icelandic kept the split alive. So "he found" and "they found" can sound nothing alike:
| Infinitive | Pret. sg (hann _) | Pret. pl (þeir _) | Supine |
|---|---|---|---|
| finna ("find") | fann | fundu | fundið |
| verða ("become") | varð | urðu | orðið |
| bíða ("wait") | beið | biðu | beðið |
Finna gives fann in the singular but fundu in the plural; verða gives varð but urðu; bíða gives beið but biðu. The singular has one vowel, the plural another, and the supine sometimes a third (orðið, beðið). This is exactly why you cite all four parts — the plural vowel is genuinely unpredictable from the singular.
Hann fann veskið sitt undir sófanum.
He found his wallet under the sofa. Preterite SINGULAR 'fann'.
Þeir fundu loksins rétta húsið.
They finally found the right house. Preterite PLURAL 'fundu' — different vowel from the singular 'fann'.
Það varð kalt um kvöldið.
It turned cold in the evening. Singular 'varð' from 'verða'.
Vinirnir urðu hissa þegar þeir sáu mig.
The friends were surprised when they saw me. Plural 'urðu' — note the vowel split varð (sg) / urðu (pl).
The present is a separate change again
One more reason the four parts matter: the present tense of many strong verbs has its own vowel, distinct from all four principal parts. Taka has the preterite tók — but in the present singular it's ég tek (with e). So taka alone shows a (infinitive), e (present sg), ó (preterite), and e again (supine tekið). The present-tense change is governed by a different rule (i-umlaut/fronting) and gets its own page; just register here that "the strong-verb vowel" is never a single thing.
Ég tek lestina klukkan átta en tók leigubíl í gær.
I take the train at eight, but took a taxi yesterday. Present 'tek' (e) vs preterite 'tók' (ó) — two different vowels from one verb.
Common Mistakes
❌ Þeir fann húsið.
Incorrect — with a plural subject you need the preterite PLURAL 'fundu', not the singular 'fann'.
✅ Þeir fundu húsið.
They found the house. Plural vowel: fundu.
❌ Hann takaði strætó. / Ég komaði heim.
Incorrect — these are strong verbs; they don't take a weak '-aði' ending. The pasts are 'tók' and 'kom'.
✅ Hann tók strætó. / Ég kom heim.
He took the bus. / I came home. Strong pasts via vowel change.
❌ Ég hef takið / komuð það.
Incorrect — the supine is its own form: 'tekið', 'komið'. You can't reuse the infinitive or the preterite plural.
✅ Ég hef tekið / komið það.
I have taken / come (to) it. Supine 'tekið' / 'komið' with 'hafa'.
❌ Það urðu kalt í gær. (with singular 'það')
Incorrect — singular subject 'það' takes the singular 'varð', not the plural 'urðu'.
✅ Það varð kalt í gær.
It turned cold yesterday. Singular 'varð'.
❌ Ég tók lestina núna. (for a present action)
Incorrect — 'tók' is the PAST. The present is 'tek': ég tek lestina núna.
✅ Ég tek lestina núna.
I'm taking the train now. Present 'tek', a different vowel from the past 'tók'.
Key Takeaways
- Strong verbs form the past by changing the stem vowel (ablaut), with no dental ending — taka → tók, never takaði.
- They have four principal parts, cited in order: infinitive – preterite singular – preterite plural – supine (taka – tók – tóku – tekið).
- The preterite singular and plural often have different vowels — fann / fundu, varð / urðu, beið / biðu — a distinction English lost. Store the past as a sg/pl pair.
- The supine (used with hafa) may have yet another vowel: orðið, beðið.
- The present tense brings a further vowel change of its own (tek vs tók) — covered separately. "The strong-verb vowel" is never just one sound.
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Start learning Icelandic→Related Topics
- Present Tense: Strong Verbs and i-UmlautA2 — Why strong verbs change their stem vowel in the present singular but not the plural — taka → ég tek, þú tekur but við tökum, þeir taka — the i-umlaut/fronting that fronts a to e, and the crucial fact that this present vowel is separate from the preterite ablaut (tek vs tók).
- The Icelandic Verb System: OverviewA1 — A map of the Icelandic verb before any conjugation — weak vs strong verbs, person/number endings, two simple tenses, the living subjunctive, the middle voice in -st, and periphrastic perfect and future.
- The Present Tense: One Form, Many MeaningsA1 — Why the Icelandic present covers what English splits across simple present, present progressive, and near future — ég les means 'I read', 'I am reading', and 'I'll read' — with the optional vera að progressive used only for emphasis.