Weak Verbs: The Four Classes

Icelandic verbs divide into two great families. Strong verbs build their past tense by changing the stem vowel — taka → tók, koma → kom — the way English does in "take → took," "come → came." Weak verbs do something English also does, but more consistently: they add a dental suffix containing d, ð, or t, exactly as English "walk → walked," "love → loved" tacks on -ed. This page is about the weak family — the larger, more regular, more predictable of the two — and the four classes it splits into. The English insight to hold onto from the start: a weak Icelandic verb is the cousin of an English "-ed" verb, and a strong one is the cousin of "sing → sang."

The signature: a dental, not a vowel change

The single thing that defines a weak verb is its preterite. Where a strong verb twists the vowel, a weak verb keeps the stem and bolts on a tooth-sound — d, ð, or t (linguists call these dental consonants because the tongue touches behind the teeth). Compare:

If you can hear a d/ð/t in the past tense, you are almost certainly looking at a weak verb. If the past is a bare vowel-shifted stem with no such consonant (tók, kom, fór), it is strong. This one test sorts the entire verb lexicon.

How the dental is spelled: ð, d, or t

The dental suffix wears three spellings, and which one appears is not random — it assimilates to the sound right before it, the same way English "-ed" is pronounced /d/ in "loved" but /t/ in "walked." The rule:

• -ð- after a voiced stem-final sound (a vowel or a voiced consonant): kalla → kallaði.
• -d- after l, m, n, r (and a few others): dæma → dæmdi, reyna → reyndi.
• -t- after a voiceless consonant (p, k, s, t): kaupa → keypti, missa → missti.

So the same underlying "past-tense tooth" surfaces as ð, d, or t purely for ease of pronunciation. You do not memorise the spelling verb by verb; you read it off the sound that precedes it. English speakers already do this unconsciously in their own language, which makes it easier than it looks.

Class 1: the -a verbs (kalla → kallaði)

The first and by far the largest class is the -a verbs: their infinitive ends in -a, their 1sg present is the bare stem (ég kalla), and their preterite is -aði. This is the powerhouse of the system.

This class is productive — it is where the language puts new verbs. Every borrowed verb joins Class 1: gúgla ("to google") → gúglaði, tvíta ("to tweet") → tvítaði, skanna ("to scan") → skannaði. That makes "-aði" your safest guess for any unfamiliar verb.

A note on borða that the umlaut guard demands: its preterite plural is borðuðum, and there is no u-umlaut here, because the stem vowel is o, not a. The -u- you see in borðuðum is just the theme vowel of the ending, not a rounded a. Only a-stem verbs round: tala → töluðum, but borða → borðuðum.

Class 2: the -i verbs (reyna → reyndi, dæma → dæmdi)

The second class has a 1sg present in -i (ég reyni, ég dæmi) and a preterite in -di / -ði / -ti — the short dental, chosen by the assimilation rule above. These verbs do not insert the -a- that Class 1 does.

Class 3: the -a verbs with -i present (duga → dugði)

A smaller third class blurs the line: the infinitive ends in -a (like Class 1), but the present behaves like Class 2, often with an -i somewhere, and the preterite takes the short dental rather than -aði. The classic example is duga ("to suffice, be enough"):

These are few enough to learn individually. The takeaway is just that an -a infinitive does not guarantee an -aði past — a handful of common verbs (duga, þora, vaka, una, vona in some treatments) take the short dental instead.

Class 4: the j-verbs that hide a vowel change (telja → taldi)

Here is the class competitors gloss over, and it is the most interesting. The Class-4 verbs — telja ("count, consider"), velja ("choose"), dvelja ("dwell, stay"), flytja ("move, transport") — are weak (they take a dental suffix), but they also change their stem vowel in the preterite, e → a, the way a strong verb would. They are weak verbs wearing a strong verb's coat.

Look at telja → taldi: there is a dental (-di), so it is weak — but the e of the stem has rounded down to a. The preterite is taldi, never teldi. This is the single most common error with this class: English speakers, having learned that weak verbs "don't change the vowel," keep the e and produce the non-word teldi. The vowel change is obligatory. Think of these four verbs as a special memorised set.

Putting the classes side by side

Set the four reference verbs together and the system snaps into focus — same dental signature, different routes to it:

Common Mistakes

The most common error is applying the -aði suffix everywhere. Only Class-1 -a verbs take -aði; Class-2 -i verbs (reyna, dæma, keyra) take -di/-ði/-ti. The present tells you: ég reyni (with -i) signals Class 2.

The Class-4 j-verbs change their vowel: telja → taldi, velja → valdi. Keeping the e (teldi) is wrong — and confusingly, teldi exists as the past subjunctive, so this slip can change your meaning entirely.

The dental assimilates to the preceding sound. After a voiceless consonant (p in kaup-) it must be -t-: keypti, not keypdi. (The vowel also shifts au→ey in this irregular verb, but the dental rule is the point here.)

U-umlaut (a → ö) only fires when the stem vowel is a. Tala (a-stem) → töluðum with ö; borða (o-stem) → borðuðum, plain o. Do not round vowels that aren't a.

Key Takeaways

• A weak verb forms its past with a dental suffix (-aði, -di, -ði, -ti); a strong verb changes its stem vowel with no suffix. The past tense is the test.
• The dental is spelled -ð / -d / -t by assimilation to the preceding sound (kallaði, reyndi, keypti) — you read it off, you don't memorise it per verb.
• Class 1 (-a → -aði) is the largest and the home of all loanwords (gúgla → gúglaði); "when in doubt, -aði."
• Class 2 (-i present → -di/-ði/-ti) covers reyna, dæma, keyra; the present -i flags the class.
• Class 4 j-verbs (telja, velja, dvelja, flytja) are weak but change the vowel e→a in the past: telja → taldi, velja → valdi. Memorise them.
• U-umlaut in the past plural fires only on a-stems (tala → töluðum), never on o/e/i/u stems (borða → borðuðum).