Learn Hardcore Icelandic: Skógurinn er rólegur á morgnana.

Formally, it is skógur + inn → skógurinn (the final -ur of skógur drops when the article is added). This -inn is the masculine singular definite ending in the nominative case.

Why isn’t there a separate word for the forest, like the in English?

Icelandic has no separate words for a/an or the:

skógur = a forest / just forest (indefinite)
skógurinn = the forest (definite)

So definiteness is normally shown by a suffix (like -inn, -an, -ið, -nir, -nar, -in, etc., depending on gender, number, and case), not by a separate article word.

What gender, number, and case is Skógurinn, and how do we know?

Skógurinn is:

Gender: masculine
Number: singular
Case: nominative

Reasons:

The dictionary form skógur ends in -ur, which is typical for masculine nouns.
It’s the subject of the sentence, so it is in the nominative case.
There is only one forest being talked about, so it is singular.
The ending -inn is the masculine nominative singular definite ending.

Why does rólegur end in -ur? What is it agreeing with?

rólegur is an adjective meaning quiet, calm. In Icelandic, adjectives agree with the noun they describe in:

gender
number
case

Here, rólegur agrees with Skógurinn:

Skógurinn = masculine, singular, nominative
So the adjective must also be masculine singular nominative: rólegur

If the noun were feminine or neuter, the ending would change:

Gatan er róleg. – The street is quiet. (feminine)
Húsið er rólegt. – The house is quiet. (neuter)

Can I say Skógurinn er rólegt or Skógurinn er róleg?

No, not with skógurinn, because its gender is masculine:

rólegur – masculine (correct here)
róleg – feminine
rólegt – neuter

You would use rólegt or róleg if the subject had a different gender:

Húsið er rólegt. – The house is quiet. (neuter)
Gatan er róleg. – The street is quiet. (feminine)

But with Skógurinn, you must say rólegur.

What’s the difference between rólegur skógur and Skógurinn er rólegur?

Both use the same adjective rólegur, but in different ways:

rólegur skógur
- Adjective right before the noun.
- Means a quiet forest (indefinite).
- Example: Þetta er rólegur skógur. – This is a quiet forest.
Skógurinn er rólegur.
- Adjective used after the verb er (is).
- Means the forest is quiet (a statement about the forest).
- Here, rólegur is a predicative adjective.

If you put the adjective before a definite noun, it usually takes a different (weak) form:

hinn rólegi skógur / rólegi skógurinn – the quiet forest

Why is it á morgnana (plural) when English says in the morning (singular)?

Icelandic often uses a plural time expression to talk about something that usually or regularly happens:

á morgnana – literally on the mornings → naturally translated as in the mornings
It implies a habit or regular situation, not just one specific morning.

Other similar expressions:

á kvöldin – in the evenings
á næturnar – at night / at nights

So Skógurinn er rólegur á morgnana means that the forest is generally quiet in the mornings, not just once.

What exactly does á morgnana mean, and what form is morgnana?

á morgnana means in the mornings or on mornings (in general) and expresses a habitual time.

morgunn = morning (masculine)
The relevant plural forms are:

Nom. pl.: morgnar
Acc. pl.: morgna
Acc. pl. definite: morgnana = the mornings

So morgnana is accusative plural definite.
With á + accusative in this time expression, á morgnana has become a fixed way to say in the mornings in general.

Why is the preposition á used instead of í in á morgnana?

Both á and í can mean something like in / at / on, but they are used differently, especially with time:

á morgnana – idiomatic expression for in the mornings (habitual)
á mánudögum – on Mondays
í morgun – this morning (earlier today, usually past)
á morgun – tomorrow

For regular, repeated times of day, Icelandic uses á + a plural time word, so you must say:

á morgnana, not í morgnana, for in the mornings.

Could I say Skógurinn er rólegur í morgnana?

No. í morgnana is not idiomatic Icelandic.

For habitual mornings, you must use á morgnana.
í is used in other time phrases, e.g. í morgun (this morning), í dag (today), í gær (yesterday), but not in this pattern.

So:

Correct: Skógurinn er rólegur á morgnana.
Incorrect: Skógurinn er rólegur í morgnana.

What tense and meaning does er express here? Does it mean right now or usually?

er is the present tense of vera (to be).

By itself, er just means is, but combined with á morgnana (a habitual time expression), it has a general / habitual meaning:

Skógurinn er rólegur á morgnana.
→ The forest is (generally) quiet in the mornings.

So it describes a typical or regular situation, not necessarily one single morning happening right now.

How would I say The forest is not quiet in the mornings?

You negate the verb with ekki:

Skógurinn er ekki rólegur á morgnana.
= The forest is not quiet in the mornings.

What is the basic word order in Skógurinn er rólegur á morgnana? Can I change it?

The basic order is:

Subject – Verb – Complement – Adverbial
Skógurinn (subject) er (verb) rólegur (adjective complement) á morgnana (time phrase)

You can move the time phrase to the front for emphasis or style, as long as the finite verb stays in second position:

Á morgnana er skógurinn rólegur. – In the mornings, the forest is quiet.

This is natural Icelandic.
A version like Rólegur er skógurinn á morgnana is also possible, but sounds more poetic or emphatic.

How do you pronounce Skógurinn er rólegur á morgnana?

A rough pronunciation guide (not strict IPA, just approximate for English speakers):

Skógurinn ≈ SKO-gu-rin
- Skó like sko in skull
  - oh (a bit like skoh)
- g is a soft, fricative sound (like a softer g/h blend)
- stress on the first syllable: SKÓ-gurinn
er ≈ ehr (like air but shorter)
rólegur ≈ ROH-le-gur
- long ó like English oh
- g again soft; the ur ending is short and unstressed
á ≈ ow in now (but a bit shorter)
morgnana ≈ MOR-gna-na
- the rg cluster is tricky; it’s something like r
  - a soft g
- again, stress on the first syllable: MOR-gnana

Main stress is always on the first syllable of each word in Icelandic.

Is rólegur closer to quiet or calm? Can it describe people as well as places?

rólegur can mean both:

quiet, peaceful (about a place or situation)
- Skógurinn er rólegur á morgnana. – The forest is quiet/peaceful in the mornings.
calm, not nervous or hyper (about a person or animal)
- Hann er mjög rólegur. – He is very calm.

So in this sentence, you can understand rólegur as quiet or peaceful; both are natural translations.