Ég athuga heimildina aftur áður en ég sendi ritgerðina.

Both are direct objects, so they are in the accusative case.

• athuga takes a direct object: athuga heimildina
• senda takes a direct object: senda ritgerðina

Both nouns are also definite:

• heimild → heimildina = the source/reference
• ritgerð → ritgerðina = the essay/paper

So the ending is showing two things at once:

1. the noun is definite
2. the noun is accusative singular

Because both heimild and ritgerð are feminine singular nouns in the accusative definite form.

A very rough breakdown is:

• heimild = source/reference
• heimildin = the source/reference
• heimildina = the source/reference, as a direct object

And the same pattern works here:

• ritgerð
• ritgerðin
• ritgerðina

In Icelandic, the definite article is usually attached to the end of the noun rather than written as a separate word like English the.

These verbs belong to different conjugation patterns.

With athuga, the 1st person singular present happens to look the same as the infinitive:

• að athuga = to check
• ég athuga = I check

With senda, the 1st person singular present is different:

• að senda = to send
• ég sendi = I send

So this is something you have to learn verb by verb. In Icelandic, the ég form is not always identical to the infinitive, but sometimes it is.

Because Icelandic often uses the present tense for actions that are future in meaning, especially when the timing is clear from context.

So ég sendi ritgerðina can mean I send the essay or I will send the essay, depending on context.

That is especially common in time clauses such as:

• áður en ég sendi... = before I send...
• þegar ég kem... = when I come...
• eftir að ég klára... = after I finish...

English can do something similar:

• I check the source again before I send the essay.

So the tense choice is normal Icelandic, not a mistake.

Áður en is a fixed expression meaning before when it introduces a full clause.

Here it connects the two actions:

• Ég athuga heimildina aftur
• áður en ég sendi ritgerðina

So the second part is a subordinate clause: before I send the essay.

It is best learned as a unit:

• áður en + clause = before + clause

Because sendi is a finite verb, not an infinitive.

Compare:

• að senda = to send → infinitive
• ég sendi = I send → finite verb

After áður en, Icelandic uses a full clause with its own subject and verb:

• áður en ég sendi ritgerðina

So að would not fit here. You are not saying before to send the essay; you are saying before I send the essay.

Because after a subordinating expression like áður en, Icelandic normally uses subject + verb order inside the subordinate clause.

So:

• áður en ég sendi ritgerðina = normal

Not:

• áður en sendi ég ritgerðina

In main clauses, Icelandic often has verb-second behavior, but subordinate clauses like this usually do not keep that same pattern.

Yes, normally you do.

Even though the subject is the same person in both parts, the second part is still a separate clause:

• Ég athuga ...
• áður en ég sendi ...

Icelandic does not usually leave the subject out here. Repeating ég is the normal and natural way to say it.

Here aftur means again.

It comes after heimildina in this sentence:

• Ég athuga heimildina aftur

That placement is very natural and means I check the source again.

You may also hear slightly different placement in Icelandic depending on emphasis, but this version is straightforward and idiomatic. In this sentence, aftur is modifying the action of checking.

It can mean several related things, depending on context.

Common meanings include:

• source or reference
• authority
• permission
• documentary evidence

In a sentence about sending an essay, learners will usually understand heimild as something like:

• source
• reference
• possibly citation

So the academic context helps determine the meaning.

Not always. Ritgerð can cover a range of written academic texts, depending on context.

Possible translations include:

• essay
• paper
• composition
• sometimes even thesis/dissertation in certain contexts

So the exact English word depends on what kind of text is being talked about. In this sentence, essay or paper would both be very natural choices.

Yes, but the meaning would change.

• heimildina / ritgerðina = the source / the essay
• heimild / ritgerð = a source / an essay, or a non-specific one

So the definite forms here suggest that the speaker means a specific source and a specific essay. That is a meaning choice, not just a grammar requirement.