When you explain why something is the case, Danish gives you a small family of conjunctions: fordi, da, eftersom, and siden. They are not interchangeable in tone, and one of them — da — also doubles as a time word, so context has to disambiguate it. This page sorts out which one to reach for, and how each behaves in the sentence.
Fordi — the neutral default ("because")
Fordi is your workhorse. It answers the question hvorfor? ("why?") directly, and it presents the reason as new information — the thing the listener didn't already know. If you are unsure which causal conjunction to use, fordi is almost always safe.
— Hvorfor kommer du ikke? — Fordi jeg er syg.
— Why aren't you coming? — Because I'm sick.
Vi blev hjemme, fordi det regnede.
We stayed home because it was raining.
Hun lærer dansk, fordi hun skal flytte til København.
She's learning Danish because she's going to move to Copenhagen.
Because fordi introduces the focal reason, it is the only one of this group that comfortably stands alone as a one-word-plus-clause answer to hvorfor?
Da — "since/as" (a known, given reason)
Da presents the reason as something already known or taken for granted — the speaker treats it as shared background, not as news. In English this is the "since" or "as" of "Since it's late, let's go home." A causal da clause very often comes first, setting up the known premise before the main point.
Da det allerede er sent, går vi hjem.
Since it's already late, we're going home.
Da du alligevel skal til byen, kan du så ikke købe mælk?
As you're going into town anyway, could you buy some milk?
Notice you would not normally answer a bare hvorfor? with da — it would sound as if you were reminding the listener of something obvious. Save da for reasons that are mutually understood.
Eftersom / siden — "since, seeing as"
Eftersom is close to da in meaning — a given, logical reason — but it is more explicit and a touch more formal. Siden ("since, seeing as") is its everyday-speech cousin and is common in casual conversation.
Eftersom du spørger, vil jeg gerne svare ærligt.
Since you ask, I'll answer honestly.
Eftersom det er din fødselsdag, bestemmer du. (formal-leaning)
Seeing as it's your birthday, you decide.
Siden du nu er her, kan vi lige så godt gå i gang. (informal)
Seeing as you're here now, we might as well get started.
Fordi vs. for — subordinating vs. coordinating
There is a second word for "because/for" — for — and it behaves completely differently in the sentence. Fordi is subordinating: it builds a subordinate clause with subordinate word order. For is coordinating (like English literary "for"): it links two main clauses, so the clause after it keeps main-clause word order, and it can never start a sentence.
Jeg går nu, for jeg er træt.
I'm leaving now, for I'm tired. (main-clause order: subject before adverb)
Jeg går nu, fordi jeg er træt.
I'm leaving now, because I'm tired.
The difference shows up the moment a sentence adverb like ikke enters: after for (coordinating) it stays after the verb; after fordi (subordinating) it moves before the verb.
Jeg ringer ikke, for jeg gider ikke.
I'm not calling, for I can't be bothered. (for + main order: 'gider ikke')
Jeg ringer ikke, fordi jeg ikke gider.
I'm not calling, because I can't be bothered. (fordi + sub order: 'ikke gider')
For the full comparison, see For vs. fordi and Coordinating conjunctions.
Word order: adverbs before the verb
Like all subordinators, fordi, da, eftersom and siden trigger subordinate word order: sentence adverbs (ikke, altid, aldrig, også, nok) come before the finite verb, not after it. This is the single most error-prone point for English speakers, whose word order doesn't move.
..., fordi jeg ikke kan komme.
...because I can't come. ('ikke' before 'kan')
..., eftersom hun aldrig svarer.
...since she never answers. ('aldrig' before 'svarer')
When a causal da/eftersom clause is fronted, the main clause inverts (verb-second rule): Da det er sent, går vi hjem — the verb går precedes its subject vi.
Common Mistakes
1. Using main-clause word order after fordi. English keeps subject–verb–adverb everywhere; Danish moves the adverb forward in the subordinate clause.
❌ Jeg kommer ikke, fordi jeg har ikke tid.
Incorrect — after 'fordi', 'ikke' must precede the verb: 'ikke har tid'.
✅ Jeg kommer ikke, fordi jeg ikke har tid.
I'm not coming because I don't have time.
2. Starting a sentence with for. For is coordinating and can only sit between two clauses, never at the front.
❌ For jeg var træt, gik jeg i seng.
Incorrect — 'for' cannot begin a sentence; use 'da' or 'fordi'.
✅ Da jeg var træt, gik jeg i seng.
Since I was tired, I went to bed.
3. Answering hvorfor? with da instead of fordi. Da presents the reason as already-known, which sounds odd as a fresh answer.
❌ — Hvorfor er du her? — Da jeg ville se dig.
Incorrect — a direct answer to 'why' takes 'fordi'.
✅ — Hvorfor er du her? — Fordi jeg ville se dig.
— Why are you here? — Because I wanted to see you.
4. Forgetting inversion after a fronted causal clause.
❌ Eftersom det regner, vi bliver hjemme.
Incorrect — the main-clause verb must come before its subject.
✅ Eftersom det regner, bliver vi hjemme.
Since it's raining, we're staying home.
Key Takeaways
- fordi = neutral "because", answers hvorfor?, presents the reason as news.
- da = "since/as", a known/given reason, often clause-initial (but also means "when" — context decides).
- eftersom / siden = "since, seeing as"; eftersom leans formal, siden is colloquial.
- for is coordinating: main-clause word order, never sentence-initial — don't confuse it with fordi.
- All the subordinators put sentence adverbs before the finite verb, and fronting a causal clause inverts the main clause.
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Start learning Danish→Related Topics
- Coordinating Conjunctions: Og, Men, Eller, For, SåA1 — The five Danish coordinators join clauses of equal rank without changing word order — plus the for vs fordi 'because' contrast and the og/at homophone trap.
- Subordinate-Clause Word OrderB1 — Danish subordinate clauses follow a different template from main clauses: no V2 inversion, and sentence adverbs like ikke come before the finite verb, not after it.
- Giving ReasonsA2 — Build Danish reason sentences with fordi, for, derfor, and da — and the different word order each one triggers.
- Subordinating Conjunctions of Time: Da, Når, MensA2 — How to say 'when', 'while', 'before', 'after' and 'until' in Danish — including the crucial da vs når split for past versus repeated events.
- For vs Fordi: Two 'Becauses'C1 — For is a coordinating 'for/because' (main-clause word order, can't start a sentence); fordi is a subordinating 'because' (subordinate word order, can start a sentence). The word-order test settles every case.