Barnið kann að synda vel.

Because barnið is the definite form: the child.

• barn = a child
• barnið = the child

In Icelandic, the definite article is usually attached to the end of the noun instead of being a separate word like English the. Here, -ið is the definite ending used with this neuter singular noun.

No. This is just grammatical gender, not biological sex.

Icelandic nouns belong to grammatical genders: masculine, feminine, or neuter. The noun barn happens to be neuter, so it takes neuter forms like barnið.

That does not tell you whether the child is a boy or a girl. It only tells you how the word behaves grammatically.

Here, barnið is nominative singular definite.

Why nominative? Because it is the subject of the sentence — the one doing the action or having the ability.

So in Barnið kann að synda vel, the subject is barnið: the child.

kann is the present tense form of the verb kunna.

In this sentence, kunna means something like:

• to know how to
• to be able to because of learned skill

So barnið kann að synda means the child knows how to swim / can swim.

This is slightly different in feel from a more general idea of ability. kunna often suggests that the ability is a skill someone has learned.

Because kunna commonly appears with að + infinitive.

So:

• kann að synda = knows how to swim / can swim

Here, að is the infinitive marker, similar to English to in to swim.

This is an important pattern to learn as a chunk:

• kunna að + infinitive

Because synda is the infinitive form, meaning to swim.

Since it comes after að, Icelandic uses the infinitive:

• að synda = to swim

So the structure is:

• kann = can / knows how
• að synda = to swim

vel is an adverb, and it means well.

It modifies the verb phrase að synda:

• synda vel = swim well

It is not describing the child; it is describing how the child swims.

Compare the English difference:

• a good swimmer → adjective-like idea
• swims well → adverb

Here Icelandic uses the adverb vel, just like English well.

This is the normal, straightforward word order for a main clause:

• Barnið = subject
• kann = finite verb
• að synda = infinitive phrase
• vel = adverb

So the sentence is built very naturally as:

The child + can/knows how + to swim + well

Also, Icelandic main clauses usually follow the verb-second pattern, meaning the finite verb tends to come early in the sentence. Since the subject comes first here, the finite verb kann comes right after it.

Yes. That is a very helpful way to understand the grammar.

A more natural English translation is often:

• The child can swim well

But a more literal breakdown is:

• Barnið = the child
• kann að synda = knows how to swim / can swim
• vel = well

So The child knows how to swim well helps show why Icelandic uses kunna að here.

Yes. Icelandic can use different verbs for ideas that English often expresses with can.

A useful basic distinction is:

• kunna (að) = know how to, be able because of learned skill
• geta = be able to, be capable of, manage to

So kunna að synda emphasizes that swimming is a skill the child has learned.

That is why kunna is a very natural choice in this sentence.