Learn Hardcore Icelandic: Hann fer á pósthúsið eftir vinnu.

fer is present tense, 3rd person singular of fara (“to go”). Present: ég fer, þú ferð, hann/hún/það fer, við förum, þið farið, þeir/þær/þau fara. Past: ég fór, við fórum, þeir fóru. So Hann fer = “He goes / is going.”

Why is it á pósthúsið and not í pósthúsið or til pósthússins?

á + accusative is the usual choice for going to many institutions and events (post office, hospital, concert). It often translates as “to.”
í + accusative also means “into/to” and is fine; it emphasizes entering the interior. Both are understood here, with á being the more idiomatic collocation.
til + genitive means “to/towards,” but it’s used more with people, towns/countries, or abstract goals. You wouldn’t typically say til pósthússins for a routine visit.

Why does pósthúsið end in -ið?

pósthús is a neuter noun. The definite singular ending for neuter in the nominative/accusative is -ið. With motion to a place (á + accusative), you get pósthús + ið → pósthúsið. For location (being there), it would be dative definite: á pósthúsinu (“at the post office”).

Do I have to use the definite form (pósthúsið)? Could I say just pósthús?

You can, but Icelandic often uses the definite form with public institutions when you “go to” them, even if not previously mentioned.

Hann fer á pósthúsið = (generic institution) “the post office.”
Hann fer í pósthús = “a post office” (some post office), less idiomatic unless you specify: í eitthvert pósthús.

Why is it accusative after á here?

With á (and í), case depends on motion vs. location:

Motion toward → accusative: á pósthúsið, í bankann.
Location (being at/in) → dative: á pósthúsinu, í bankanum. Since fer expresses motion, accusative is used.

What case is vinnu in eftir vinnu, and why?

The form vinnu is the oblique singular of vinna (“work”)—for this noun, accusative and dative singular look the same. eftir can govern different cases depending on meaning; in time expressions (“after”), speakers commonly use this oblique form. Here, you can safely learn it as the fixed time phrase eftir vinnu = “after work.”

Does eftir always take the same case?

No. It varies with meaning:

Dative uses include “after (in time), according to, by (authorship), along”: eftir vinnu; saga eftir Jón.
Accusative uses include “in search of / to fetch / on someone’s trail”: Ég kem eftir þig (“I’ll come pick you up”), and often with specified durations: eftir tvo daga (“after two days”). With vinna, the form vinnu covers both acc/dat, so the form doesn’t change.

Can I move eftir vinnu to the front?

Yes. Icelandic is verb-second (V2). If you front an adverbial, the finite verb remains second:

Eftir vinnu fer hann á pósthúsið. This is natural and emphasizes the time frame.

Is Hann fer eftir vinnu á pósthúsið also correct, or must time come last?

It’s correct. Adverbial order is fairly flexible. Both

Hann fer á pósthúsið eftir vinnu and
Hann fer eftir vinnu á pósthúsið are fine; choose based on emphasis.

Does Hann fer mean a habit or a specific plan for today?

Context decides. Icelandic present can be:

Habitual: “He usually goes to the post office after work.”
Near-future/scheduled: “He’s going to the post office after work (today).” The time phrase makes the meaning clear.

Can I omit Hann (the subject), like in some other languages?

No. Modern Icelandic generally requires overt subject pronouns. You say Hann fer ..., not just Fer ... (except in imperatives or special constructions).

How do I pronounce the tricky bits?

Approximation:

Hann = “hahn” (short a).
fer = “fehr” (like “fair” without the y-glide).
á = “ow” (as in “cow”).
póst- = “poust” (ó like English “o” in “go,” a bit tenser).
-húsið = “hoo-sith” (final ð like soft “th” in “this”).
Altogether: “HAHN fehr ow POUST-hoo-sith.”

Could I use a more specific motion verb than fara?

Yes:

Hann gengur á pósthúsið = He walks to the post office.
Hann keyrir á pósthúsið = He drives to the post office.
Colloquial: Hann labbar á pósthúsið = He walks to the post office. fara is neutral (“go”).

Why not say eftir að vinna for “after work”?

Because eftir að must be followed by a finite clause, not a bare infinitive. Use:

The noun phrase: eftir vinnu (“after work”).
Or a finite clause (often perfect): eftir að hann er búinn að vinna (“after he has finished working”).

Could I say úr vinnu instead of eftir vinnu?

They differ:

eftir vinnu = “after work” (time reference).
úr vinnu = “from work” (source/origin). Use with verbs of coming: Hann kemur úr vinnu (“He comes from work”). With fara (“go”), stick to eftir vinnu.

How do I say “He is at the post office” vs. “He is in the post office”?

Use dative for location:

“at”: Hann er á pósthúsinu.
“in/inside”: Hann er í pósthúsinu. Both are possible; á treats it as an institution you attend, í highlights the interior.

What does the compound pósthús literally mean, and where does the article go?

pósthús = póst (“post/mail”) + hús (“house”). Icelandic attaches the definite article as a suffix to the noun: pósthús + ið → pósthúsið. Stress stays on the first syllable of the word: PÓST-hú-sið.