Learn Hardcore Icelandic: Um kvöldið slaka ég á í sófanum og hlusta á tónlist. - In the evenings I relax on the sofa and listen to music.

um is a preposition that, with time expressions, often means “around / during / in” (talking about when something happens).
kvöldið is “the evening” (from kvöld, “evening”, plus the definite ending -ið).

If you said only Kvöldið slaka ég á…, it would sound like you’re talking about one specific evening that was already mentioned.
Um kvöldið is more like a general time-of-day phrase: In the evening (as a rule / typically) I relax…

What case is kvöldið in, and why that case?

kvöldið is in the accusative singular, definite.

Base form: kvöld (neuter, “evening”).
Definite singular: kvöldið (“the evening”).
The preposition um normally takes the accusative case, so you get um kvöldið.

Because neuter nouns have the same form for nominative and accusative in the singular, kvöldið looks like “nominative + accusative”, but here it’s accusative because of um.

Could I also say Á kvöldin slaka ég á…? How is that different from Um kvöldið…?

Yes, Á kvöldin slaka ég á í sófanum og hlusta á tónlist is also correct, but it’s slightly different:

Um kvöldið = “in the evening” (as a time of day; in general speech it can be habitual).
Á kvöldin = literally “on the evenings”, idiomatically “in the evenings / in the evenings in general”, clearly habitual or repeated.

Nuance:

Um kvöldið can be understood as “(at) evening time (I usually…)”.
Á kvöldin makes the habitual sense very explicit: it’s what you do in the evenings as a rule.

Both can be used in a sentence talking about routine; Á kvöldin just emphasizes the “every/most evenings” feeling a bit more.

Why is the word order slaka ég á and not ég slaka á?

Icelandic is mainly a verb-second (V2) language in main clauses. That means:

The finite verb (here: slaka) must be in second position in the clause.
The element before the verb can be almost anything (subject, time phrase, place phrase, etc.), but the verb still comes second.

In your sentence:

Um kvöldið – first constituent (a time phrase).
slaka – the finite verb, in second place.
ég á í sófanum og hlusta á tónlist – the rest of the clause.

So:

✅ Um kvöldið slaka ég á… – correct V2 order.
✅ Ég slaka á um kvöldið… – also correct; now the subject is first and the time phrase comes later.
❌ Um kvöldið ég slaka á… – wrong, because the verb is not in second position.

What exactly is slaka á? Is á a preposition with an object here?

slaka á is a fixed verb phrase meaning “to relax, to unwind”. You should treat slaka á as a kind of phrasal verb:

slaka alone usually means something like “to loosen, slacken” (e.g. a rope).
With á, slaka á becomes “to relax” (mentally/physically).

In this usage:

á does not have its own object; it is more like a particle attached to the verb.
You can say simply: Ég slaka á. – “I relax.”

So in slaka ég á í sófanum, the á belongs tightly to slaka. You cannot split it off or attach it to sófanum:

✅ slaka ég á í sófanum
❌ slaka ég í sófanum á

The preposition á does take an object in other expressions (like hlusta á tónlist), but not in slaka á.

The word á appears twice in the sentence. Does it mean the same thing in slaka á and hlusta á tónlist?

Grammatically, they behave differently, even though it’s the same word á:

slaka á
- Here á is part of a phrasal verb “to relax”.
- It does not introduce any object.
- You can’t replace it with another preposition; slaka á is just a fixed combination.
hlusta á tónlist
- Here á does function as a normal preposition, usually translated “to” in this context.
- The verb hlusta á means “to listen to”, and á takes an object in the accusative.
- tónlist is that object: you “listen to music”.

So:

slaka á ≈ “relax” (no object).
hlusta á [something-ACC] = “listen to [something]” (with an object).

Why is it í sófanum and not just í sófa or í sófi? What case is this?

í sófanum literally means “in the sofa”, but idiomatically “on the sofa / on the couch”.

Breakdown:

Base noun: sófi – “sofa, couch” (masculine).
Dative singular: sófa.
Definite dative singular: sófanum – “in/on the sofa”.

The preposition í (“in”) has two main patterns:

í + accusative for movement into something (into the house).
í + dative for location inside/at something (in the house).

Here we describe location (where you are relaxing), so we use dative:

í sófanum = í (in/at) + sófanum (dative definite “the sofa”).

You could say í sófa without the article, which would be “in/on a sofa”, i.e. indefinite.

Can I say á sófanum instead of í sófanum?

Yes, á sófanum is grammatically correct and understandable:

á sófanum = “on the sofa”.
í sófanum = literally “in the sofa”, but commonly used like English “on the sofa / on the couch”.

In everyday Icelandic, í sófanum is very natural when talking about sitting/lying on a sofa. Á sófanum can sound a bit more literally “on top of” it, but many speakers would accept both.

So:

Um kvöldið slaka ég á í sófanum… – very idiomatic.
Um kvöldið slaka ég á á sófanum… – possible, but less common style-wise.

How does hlusta á tónlist work grammatically? Why do we need á here?

hlusta á is another fixed verb–preposition pair, and together they mean “to listen to”:

hlusta = “to listen” (intransitive by itself).
hlusta á [object-ACC] = “to listen to [object]”.

In the sentence:

hlusta á tónlist = “(I) listen to music”.
tónlist is the direct object in the accusative case, governed by á.

You cannot drop á if you mention what you’re listening to:

✅ Ég hlusta á tónlist. – I listen to music.
❌ Ég hlusta tónlist. – not idiomatic; sounds wrong.

So it may help to memorize hlusta á as a unit: “listen to”.

Why is tónlist used without a definite article, when other nouns here are definite (kvöldið, sófanum)

tónlist is a mass noun (“music”) and is often used without an article when speaking in general:

hlusta á tónlist = “listen to music (in general)”.

Compare:

hlusta á tónlistina = “listen to the music”, i.e. some specific music that you and the listener already know about (for example, “the music we put on earlier”).

By contrast:

kvöldið – here it’s the conventional way to talk about time of day: um kvöldið (“in the evening”).
sófanum – you’re referring to a specific, known sofa (e.g. in your home).

So the pattern here is:

Time-of-day phrase: um kvöldið.
Specific location: í sófanum.
General activity/object type: (hlusta á) tónlist (no article, general “music”).

Why isn’t ég repeated before hlusta? Could I say …og ég hlusta á tónlist?

Both versions are grammatically correct:

Um kvöldið slaka ég á í sófanum og hlusta á tónlist.
Um kvöldið slaka ég á í sófanum og ég hlusta á tónlist.

In Icelandic, when two clauses share the same subject (here, ég) and the same tense, it is very natural to omit the second subject after og (“and”):

The listener easily understands that ég is the subject of both slaka and hlusta.

Including ég a second time (…og ég hlusta…) can be used for extra emphasis or contrast, but in a neutral sentence like this it’s smoother and more typical without repeating it.