Ég undirstrika andlagið í setningunni.

In Icelandic, the definite article is usually attached to the end of the noun instead of standing as a separate word.

So:

• andlag = object
• andlagið = the object

The ending -ið is the definite article here. This is very common in Icelandic.

Because it contains both:

• the noun setning = sentence
• the definite article = the
• a case ending

Here, setningunni means the sentence in the dative singular.

Breaking it down roughly:

• setning = sentence
• -unni = the dative singular definite ending for this noun

So í setningunni means in the sentence.

The preposition í can take either:

• accusative when it means movement into
• dative when it means location in

Here the meaning is location: in the sentence, not into the sentence.
So Icelandic uses the dative:

• í setningunni = in the sentence

This is a very important pattern in Icelandic.

Here andlagið is the direct object of the verb undirstrika, so it is in the accusative.

However, with a neuter noun like andlag, the nominative and accusative singular often look the same. So even though the function is accusative, the form andlagið does not visibly change.

That means:

• function: accusative object
• form: looks the same as nominative

This happens often with neuter nouns in Icelandic.

Yes, normally undirstrika takes a direct object in the accusative.

So in this sentence:

• ég = subject
• undirstrika = verb
• andlagið = accusative direct object

That is a very standard sentence pattern.

Because many Icelandic verbs have a 1st person singular present form that looks the same as the infinitive without að.

So:

• að undirstrika = to underline
• ég undirstrika = I underline

The infinitive usually appears with að, but the finite verb in the sentence does not.

Normally, yes, you should include ég.

Unlike some languages, Icelandic usually keeps the subject pronoun in ordinary sentences:

• Ég undirstrika andlagið í setningunni.

Leaving out ég would usually sound incomplete unless the context is very special, such as notes, headings, or certain informal situations.

This sentence has a very normal Icelandic main-clause word order:

• Ég = subject
• undirstrika = verb
• andlagið = object
• í setningunni = prepositional phrase

So the pattern is basically:

Subject + Verb + Object + Prepositional phrase

Icelandic is also a verb-second language, which means the finite verb tends to come second in main clauses. Since the subject is first here, the verb naturally comes right after it.

Andlag is the Icelandic grammar term for object.

In many learning contexts, it usually refers to the grammatical object of a verb. Depending on the context, English grammar might distinguish between direct object and indirect object, but andlag is the general Icelandic word learners often meet first for object.

So in this sentence, andlagið means the object in a grammatical sense, not a physical object like a thing on a table.

Because Icelandic usually puts the onto the noun itself.

So instead of using a separate article like English does:

• the object
• the sentence

Icelandic usually says:

• andlagið
• setningunni

This is one of the first big differences English speakers notice.

Here í means in.

But Icelandic prepositions are strongly connected to case, so you usually have to learn both:

• what the preposition means
• which case it takes in different situations

With í:

• í
  • accusative = into
• í
  • dative = in

In this sentence, it is clearly the location meaning, so it uses the dative: í setningunni.

The accents in Icelandic are not just stress marks; they are part of the spelling and usually indicate a different vowel sound.

A simple learner-friendly guide here is:

• ég sounds roughly like yeg with a y sound at the start
• í sounds like ee
• undirstrika has stress on the first syllable: UN-dir-stri-ka

The accents matter, so i and í are not the same vowel.

Yes, you can, but then Icelandic word order changes because of the verb-second rule.

For example:

• Í setningunni undirstrika ég andlagið.

That is possible and means the same basic thing, but with extra focus on in the sentence.

Notice that when Í setningunni comes first, the verb undirstrika still stays in second position, and ég moves after the verb.

Grammatical gender in Icelandic is partly predictable, but often you simply have to learn it with each noun.

Icelandic nouns belong to one of three genders:

• masculine
• feminine
• neuter

Here:

• setning is feminine
• andlag is neuter

Gender affects articles, adjective endings, and case endings, so it is very useful to memorize each noun together with its gender from the beginning.

You would remove the definite article ending.

So:

• í setningunni = in the sentence
• í setningu = in a sentence

Likewise:

• andlagið = the object
• andlag = an object / object

This shows how important the endings are in Icelandic: they carry information that English often expresses with separate words.