Ég sé hundinn fyrir aftan húsið.

A quick breakdown:

• Ég = I
• sé = see
• hundinn = the dog
  
  • specifically, dog as the direct object
• fyrir aftan = behind
• húsið = the house

So the structure is basically:

• subject: Ég
• verb: sé
• object: hundinn
• prepositional phrase: fyrir aftan húsið

A very natural gloss is:

• I see the dog behind the house.

Because sjá is the infinitive, meaning to see.

In the sentence, you need the verb form that matches I, so Icelandic uses the 1st person singular present:

• að sjá = to see
• ég sé = I see

Some present-tense forms of sjá are:

• ég sé = I see
• þú sérð = you see
• hann/hún/það sér = he/she/it sees
• við sjáum = we see

So Ég sé is simply the correct conjugated form.

Because hundinn is the form used for the dog when it is the direct object of the verb.

Here, the dog is what is being seen, so it is in the accusative case.

Compare:

• hundur = dog or a dog in the nominative form
• hundinn = the dog in the accusative singular

A useful comparison:

• Hundurinn sér mig. = The dog sees me.
  
  • hundurinn is the subject, so nominative
• Ég sé hundinn. = I see the dog.
  
  • hundinn is the object, so accusative

So the short answer is:

• hundur = subject form
• hundinn = object form, with the

In Icelandic, the is often added to the end of the noun instead of being written as a separate word.

So:

• hundur = dog
• hundinn = the dog

and

• hús = house
• húsið = the house

This is called the suffixed definite article.

So unlike English:

• English: the dog
• Icelandic: hundinn

Because the sentence needs the accusative form, not the nominative form.

For hundur:

• hundurinn = the dog as a subject
• hundinn = the dog as an object

Since in Ég sé hundinn, the dog is being seen, it is the object, so hundinn is correct.

This is a very common pattern in Icelandic: the noun changes form depending on its role in the sentence.

Because fyrir aftan takes the accusative case, and the accusative singular definite form of hús is húsið.

For hús:

• húsið = the house, nominative/accusative singular
• húsinu = the house, dative singular

So after fyrir aftan, Icelandic uses:

• fyrir aftan húsið = behind the house

A detail that often confuses learners: with many neuter nouns, the nominative and accusative look the same. So even though húsið looks like a basic form, here it is functioning as accusative.

It is best to learn fyrir aftan as a single unit meaning behind.

Even though it has two words, in practice learners should treat it like a set expression or compound preposition.

So memorize:

• fyrir aftan = behind

rather than trying to translate each piece separately every time.

This is common in Icelandic. Some location expressions are made of more than one word but function as one preposition-like phrase.

In this sentence, the most natural reading is that it describes where the dog is:

• I see the dog [that is] behind the house.

That is also the most likely interpretation in English for I see the dog behind the house.

Could context make things ambiguous? Sometimes, yes. But as written, the normal understanding is:

• the dog is behind the house
• I can see it there

This sentence uses a very normal, neutral word order:

• Ég = subject
• sé = verb
• hundinn = object
• fyrir aftan húsið = location phrase

So the pattern is basically:

• Subject + Verb + Object + Phrase

That is a very common order in simple Icelandic main clauses.

Icelandic word order can be more flexible than English, especially for emphasis or style, but this version is the plain, straightforward one a learner should be comfortable with first.

Because in Icelandic, accented vowels are part of the normal spelling system. They are not optional decoration.

For example:

• e and é are different letters
• u and ú are different letters

So you should learn the accented forms as part of the word itself:

• ég
• sé
• hús
• húsið

These accents affect pronunciation and are important in correct spelling.

Yes, but the meaning would change.

Compare:

• Ég sé hundinn fyrir aftan húsið. = I see the dog behind the house.
• Ég sé hund fyrir aftan hús. = I see a dog behind a house.

So the definite endings matter:

• -inn on hundinn = the
• -ið on húsið = the

Without them, the nouns are indefinite, more like a dog and a house.