Learn Hardcore Icelandic: Ef ég sef lengur, þá fer höfuðverkurinn. - If I sleep longer, then the headache goes away.

With it: Ef ég sef lengur, þá fer höfuðverkurinn.
Without it: Ef ég sef lengur, fer höfuðverkurinn. In both versions, the finite verb in the main clause must still come early (see the verb‑second point below).

Why does the verb come before the subject in the second clause (þá fer höfuðverkurinn)?

Icelandic main clauses are verb‑second (V2). Something occupies first position (here þá), so the finite verb (fer) must be second, and the subject (höfuðverkurinn) follows:

Ef ég sef lengur, þá fer höfuðverkurinn. If you drop þá, the first slot of the main clause is effectively taken by the preceding ef‑clause, so the verb still comes right away:
Ef ég sef lengur, fer höfuðverkurinn.

Do I need the comma after the ef‑clause?

It’s standard and safest to include it: Ef ég sef lengur, … Modern “light‑comma” styles sometimes omit it, but most careful writing keeps it. You’ll see both in real life.

Why is the present tense used for a future result? Could I say mun?

Icelandic typically uses the present for future time in conditionals: Ef ég sef lengur, (þá) fer…
You can use mun for a more explicitly predictive or formal tone:

Ef ég sef lengur, þá mun höfuðverkurinn fara. The version with plain present is the most natural everyday choice.

What’s the difference between lengi, lengur, seinna, and meira?

lengi = for a long time (duration). Example: Ég sef lengi (I sleep for a long time).
lengur = longer (duration; comparative of lengi). Example: Ég sef lengur (I sleep longer).
seinna = later (later point in time). Example: Ég vakna seinna (I wake up later).
meira = more (quantity/amount). Example: Ég sef meira (I sleep more overall), not necessarily “wake later.”
In this sentence, lengur is correct because we’re comparing duration.

Does sofa mean “to fall asleep”? How is it different from sofna?

sofa = to sleep. Present: ég sef, þú sefur, hann/hún sefur, við sofum …
sofna = to fall asleep. Present: ég sofna, þú sofnar, hann/hún sofnar, við sofnum …
The sentence uses sef (I sleep), not “fall asleep.”

Is þá just the same as English “then”? Could I use svo?

After ef, þá is the default correlative “then.” You can omit it, but you wouldn’t use svo in that slot. svo is more like narrative “then/so” and typically starts a new step or sentence. So use either:

Ef …, þá … or
Ef …, … (verb second) …

Why is it höfuðverkurinn (with the definite ending)?

Icelandic marks definiteness with a suffix, so höfuðverkurinn = “the headache.” It’s definite because you’re talking about a particular, current headache. An indefinite layout is common in other frames, e.g. Ég er með höfuðverk (“I have a headache”).

Is there a difference between höfuðverkur and höfuðverk?

Both are used for “headache.” In statements like “I have a headache,” Ég er með höfuðverk is very common. When you make it definite as a subject, höfuðverkurinn is the standard form: … fer höfuðverkurinn.

Could I use another verb instead of fer for “goes away”?

Yes, several idiomatic options:

… hverfur höfuðverkurinn. (disappears; a bit stronger)
… hjaðnar höfuðverkurinn. (subsides)
… dregur úr höfuðverknum. (it lessens; literally “it draws out of the headache” — needs the dative höfuðverknum) All are natural depending on nuance.

Where does the negation ekki go?

Place ekki right after the finite verb of its clause:

Subordinate: Ef ég sef ekki lengur, …
Main clause: …, þá fer höfuðverkurinn ekki.

Can I swap the order of the clauses?

Yes:

Höfuðverkurinn fer, ef ég sef lengur.
Ef ég sef lengur, fer höfuðverkurinn.
Ef ég sef lengur, þá fer höfuðverkurinn. All are fine (with the usual V2 word order in the main clause).

How do I pronounce the tricky letters in this sentence?

Rough guide:

þá: initial þ like unvoiced English “th” in “thin”; á like “ow” in “cow.”
höfuð-: ö is like the vowel in British “bird,” but rounded; ð is a soft “th” sound, and in höfuðverk- it’s often very light or dropped in fast speech.
ef: the final f sounds like a v, so roughly “ev.”
lengur: the “ng” is like “sing,” not “finger.”
Stress is on the first syllable of each word: Ef | ég | sef | lengur, | þá | fer | höfuðverkurinn.

What are the key forms of sofa and fara I should know?

sofa (to sleep): present ég sef; past ég svaf; past plural við sváfum; past participle sofið.
fara (to go): present ég fer; past ég fór; past plural við fórum; past participle/supine farið.

Should I ever use þegar instead of ef here?

Use ef for an if/condition. Þegar means “when/whenever” (temporal). You could say Þegar ég sef lengur, (þá) fer höfuðverkurinn, which frames it as a general time‑based statement; ef presents it as a condition.

Is the colloquial ef að acceptable?

You’ll hear ef að in speech. In careful writing, most teachers/editors prefer the plain ef (no að).