skulu is the Icelandic auxiliary of commitment and command — the one English collapses into "shall / will" alongside three other ideas. Its single most important property is one almost every textbook underplays: skal is a performative. When you say ég skal, you are not predicting anything and you are not describing a plan — you are giving your word. When you say þú skalt, you are not forecasting the other person's future — you are telling them to do it. Like munu, skulu is a defective preterite-present: it has a present and a past subjunctive, takes a bare infinitive (no að), and has no supine and no participle. Getting it right is mostly about not confusing it with munu (prediction) and ætla að (intention).
Conjugation
Type: preterite-present (the archaic class of kunna, muna, eiga, mega, munu), defective. Followed by a bare infinitive: ég skal hjálpa þér "I'll help you." There is no supine, no past participle, no present participle in normal use. Note the u-umlaut in the present plural: við skulum (the u-ending pulls the stem vowel, and the verb is simply lexicalised with u throughout the plural).
| Principal parts | |
|---|---|
| Infinitive | að skulu |
| 1sg present | skal |
| 1sg past (subjunctive) | skyldi |
| Supine | — (none) |
| Past participle | — (none) |
| Person | Present (nútíð) | Past / subjunctive (þátíð vmh.) |
|---|---|---|
| ég | skal | skyldi |
| þú | skalt | skyldir |
| hann / hún / það | skal | skyldi |
| við | skulum | skyldum |
| þið | skuluð | skylduð |
| þeir / þær / þau | skulu | skyldu |
Read the present singular carefully: ég skal, þú skalt, hann skal — 1st and 3rd person are bare skal with no ending, and the 2nd person adds -t (skalt), the signature preterite-present pattern, never -ur. The plural carries u throughout: skulum, skuluð, skulu.
The past set functions as a past subjunctive — "should, was to, were to" — and is spelled with y: skyldi, skyldir, skyldi, skyldum, skylduð, skyldu. Mind the y: it is skyldi, never skildi (that would be the verb skilja "understand/separate"). Because skulu is defective, there is no separate past indicative; the "past" of skulu simply is this skyldi set. There is likewise no present subjunctive in living use distinct from the indicative, and no imperative (you cannot command someone to "shall").
skal in the first person: a promise
This is the heart of the verb. Ég skal + infinitive is a performative commitment: by uttering it you take on the obligation. It is the natural Icelandic for "I'll do it, you have my word," "leave it to me," "I promise I will." It is markedly stronger and more personal than ég mun (a detached prediction) or ég ætla að (a stated plan).
Ég skal hjálpa þér að flytja, engar áhyggjur.
I'll help you move, don't worry. — skal = a personal undertaking. You are promising, not forecasting.
Ég skal redda þessu, ég lofa.
I'll sort this out, I promise. — skal pairs naturally with ég lofa 'I promise' because both express commitment.
Þú skalt fá peningana þína á morgun — það er á hreinu.
You'll have your money tomorrow — that's settled. — here skalt is the speaker's guarantee to the listener, an assurance about an outcome.
þú skalt in the second person: a command
Aimed at the listener, þú skalt is not a prediction about what they will do — it is a directive: "you are to, you'd better, do this." It is firmer than the bare imperative and is exactly how you give a strong instruction, a warning, or pointed advice. Tone of voice decides whether it lands as friendly counsel or as a threat.
Þú skalt fara til læknis ef þetta lagast ekki.
You should go to the doctor if this doesn't get better. — firm advice: 'you are to go'. Stronger than a gentle ættir.
Þú skalt aldrei gera þetta aftur.
You are never to do this again. — a command/warning. The performative force is unmistakable here.
við skulum = "let's"
The first-person plural við skulum + infinitive is the standard hortative "let's …" — a proposal that includes the speaker. This is one of the highest-frequency uses of the whole verb and the form you will reach for daily.
Við skulum hittast klukkan átta fyrir utan bíóið.
Let's meet at eight outside the cinema. — við skulum + bare infinitive = 'let's meet'.
Skulum við bara panta pitsu í kvöld?
Shall we just order pizza tonight? — fronted Skulum við …? is the question 'shall we …?', proposing a plan together.
skyldi: "should / was to / were to"
The past skyldi does several jobs. As a past-of-obligation it means "was/were to, was supposed to" in reported or narrative contexts (ég vissi ekki hvað ég skyldi gera "I didn't know what I was to do"). It also appears in indirect questions and exclamatory wonderings (hver skyldi hafa gert þetta? "who could have done this, I wonder?"). It is more bookish than the everyday átti að "was supposed to," but you will meet it constantly in writing.
Ég vissi ekki hvað ég skyldi segja við hana.
I didn't know what I should say to her. — skyldi = 'was to / should' in an indirect question about obligation.
Hver skyldi hafa skilið hurðina eftir opna?
Who could have left the door open, I wonder? — skyldi here colours the question with wonder/speculation, a very idiomatic use.
skulu vs munu vs ætla: the contrast that matters
English "I'll come" hides three different Icelandic meanings, and choosing wrongly is the most common error learners make with all three auxiliaries:
| Auxiliary | Core meaning | "I'll come" |
|---|---|---|
| skulu | commitment / command | ég skal koma — I'll come (you have my word) |
| munu | prediction / expectation | ég mun koma — I will come (forecast; formal) |
| ætla (að) | intention / plan | ég ætla að koma — I'm going to come (my plan) |
For an ordinary stated plan in conversation, ætla að is the default. Reach for skulu only when you genuinely mean to commit (a promise, a guarantee) or to direct (an instruction). Reach for munu for forecasts and elevated written "will." The mismatch English speakers fall into is using skulu as a neutral future — but every skal carries that performative weight.
Common Mistakes
❌ Ég skal rigna á morgun.
Wrong sense — skulu is commitment/command, not a forecast. The weather can't promise anything; a prediction needs munu: það mun rigna.
✅ Það mun rigna á morgun.
It will rain tomorrow.
The rain isn't undertaking an obligation. Forecasts take munu (or simply the present tense), never skulu.
❌ Ég skal fara í ræktina eftir vinnu, það er planið.
Odd — for a personal plan ('it's the plan'), intention ætla að fits, not the promise skal. skal turns it into a vow to someone.
✅ Ég ætla að fara í ræktina eftir vinnu.
I'm going to go to the gym after work.
A plan you're merely announcing is ætla að; skal makes it a commitment to a listener.
❌ Ég skal að hjálpa þér.
Incorrect — skulu takes a BARE infinitive, no að. It's skal hjálpa, never skal að hjálpa.
✅ Ég skal hjálpa þér.
I'll help you.
Like the other preterite-present modals, skulu is followed directly by the infinitive with no linking að.
❌ Ég hef skulað klára þetta.
Incorrect — skulu has NO supine; you cannot build a perfect with it. It is defective: present skal and past subjunctive skyldi only.
✅ Ég skal klára þetta.
I'll finish this. (past obligation: ég vissi að ég skyldi klára það — I knew I was to finish it.)
There is no skulað. Treating skulu as a full verb with a perfect is a structural error.
❌ Ég vissi ekki hvað ég skildi gera.
Spelling error — the past of skulu is skyldi with y; skildi with i is the verb skilja 'understand/separate'.
✅ Ég vissi ekki hvað ég skyldi gera.
I didn't know what I should do.
The y/i contrast is meaningful here: skyldi (was to) versus skildi (understood). The accent-and-vowel rules of Icelandic make these two completely different words.
Key Takeaways
- skulu is the defective auxiliary of commitment/command: present skal / skalt / skal / skulum / skuluð / skulu, past subjunctive skyldi / skyldir / skyldi / skyldum / skylduð / skyldu. No supine, no participle, no imperative.
- skal is a performative: 1st person = a promise (ég skal koma, you have my word); 2nd person = a command (þú skalt fara, you are to go).
- við skulum
- bare infinitive = "let's" — an everyday, high-frequency use.
- skyldi (with y) = "should / was to / were to," and colours wondering questions (hver skyldi …?). Don't write skildi (that's skilja).
- It takes a bare infinitive (no að). Keep the trio apart: skulu = commitment/command, munu = prediction, ætla að = intention. For ordinary spoken plans, use ætla að.
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- mega, kunna, skulu, munuB1 — Four Icelandic modals beyond geta and vilja: mega 'be allowed/may' (þú mátt fara), kunna 'know how to / might' (ég kann að synda; kann að vera 'maybe'), skulu 'shall — commitment or command' (ég skal hjálpa, þú skalt fara), and munu 'will — neutral prediction' (það mun rigna). The key nuance: skal in the 1st person is a PROMISE and in the 2nd a directive — a performative force English 'shall' has lost — while munu is a detached prediction.
- munu vs skulu vs ætla: Future and IntentionB2 — English 'will / shall / going to' splits across three Icelandic verbs. munu makes a neutral PREDICTION ('it will rain', formal future); skulu expresses the speaker's COMMITMENT — a promise in the 1st person, a command in the 2nd ('I'll definitely help', 'you shall go'); ætla að states an INTENTION or plan ('I'm going to study tonight'). The key is that skal is performative — saying it commits you — a force English 'shall' has mostly lost, so ég skal is stronger than 'I will', and munu is a forecast, never a plan. Includes a decision table.
- The Imperative and CommandsA2 — How to give orders, requests, and instructions — the bare-stem imperative, the everyday spoken -ðu/-du/-tu clitic that fuses the pronoun þú (komdu, farðu, gefðu), the plural/polite form built on the 2pl (komið, talið), the 'let's' förum, and softeners like nú and vinsamlegast.
- munuB1 — Full paradigm of the defective future auxiliary munu 'will' — a preterite-present verb with only a present (mun/munt/mun/munum/munuð/munu) and a past subjunctive (myndi…), no supine and no participle. munu predicts ('it will rain'); its past form myndi is the everyday 'would' of conditionals. Distinguishing it from skulu (commitment/obligation) and ætla (intention) is the key to using it correctly.
- ætla (to intend / be going to)A2 — Full conjugation of the weak Class-1 verb ætla (ætla / ætlaði / ætluðu / ætlað), the everyday near-future construction ætla að + infinitive, the reflexive ætla sér, and how it differs from vilja and munu.