Við lagfærum skattstofninn því að fjármagnstekjurnar eru rangar.

Lagfærum is the present tense, 1st person plural form of the verb lagfæra.

So:

• ég lagfæri = I fix / amend
• við lagfærum = we fix / amend

The ending -um is a common we ending in Icelandic present tense verbs.

Icelandic often allows the subject pronoun to be dropped less freely than Spanish or Italian, so keeping við is normal and clear. It explicitly tells you the subject is we.

In some contexts, the verb form alone might make the meaning obvious, but við is completely natural here.

Skattstofninn is the noun skattstofn with the definite article attached.

Breakdown:

• skattstofn = tax base / taxable base
• -inn = the

So skattstofninn means the tax base.

This is a very typical Icelandic pattern: instead of a separate word for the, Icelandic usually adds the article to the end of the noun.

Because Icelandic uses a suffixed definite article.

Compare:

• skattstofn = a tax base / tax base
• skattstofninn = the tax base

The ending changes depending on gender, number, and case. Here, -inn is the masculine singular definite form.

Yes. It is the direct object of lagfærum, so it is in the accusative.

That said, for this noun, the definite singular form looks the same here as the nominative form, so you do not see a visible change. Icelandic learners often notice that case is not always obvious just from the ending.

Here því að means because.

It introduces the reason:

• Við lagfærum skattstofninn = we amend the tax base
• því að fjármagnstekjurnar eru rangar = because the capital-income figures are incorrect

So the whole sentence has a clear main clause + reason clause structure.

No. In this sentence, að is part of the conjunction því að = because.

So this is not the infinitive marker.

Compare:

• að lesa = to read → infinitive marker
• því að = because → conjunction

Same spelling, different function.

Because tekjur is normally a plural noun in Icelandic.

So even where English might use something like income as an uncountable singular idea, Icelandic often uses plural tekjur = earnings / revenues / income.

Therefore:

• fjármagnstekjur = capital income / capital earnings
• fjármagnstekjurnar = the capital-income figures / the capital earnings

Because the sentence is talking about specific capital-income figures, not capital income in general.

So:

• fjármagnstekjur = capital income in general
• fjármagnstekjurnar = the capital-income figures in this case

Likewise:

• skattstofn = tax base in general
• skattstofninn = the specific tax base being discussed

English and Icelandic do not always use definiteness in exactly the same situations, so this is a good thing to notice.

Because rangar agrees with fjármagnstekjurnar.

The noun tekjur is:

• feminine
• plural

So the adjective must also be:

• feminine plural

That gives:

• rangar = incorrect / wrong

This is a classic Icelandic agreement pattern. Unlike English, adjectives change form to match the noun.

Because predicate adjectives in Icelandic still agree with the subject.

In:

• fjármagnstekjurnar eru rangar

rangar is a predicate adjective after vera (to be), but it still matches the subject fjármagnstekjurnar in gender and number.

English does not do this:

• the income figures are wrong
• the book is wrong
• the statements are wrong

Icelandic does:

• rangur / röng / rangt / rangar, etc., depending on what is being described.

The sentence has two clauses:

1. Við lagfærum skattstofninn
2. því að fjármagnstekjurnar eru rangar

In the main clause, the order is straightforward:

• subject við
• verb lagfærum
• object skattstofninn

In the því að clause, you also get normal order:

• subject fjármagnstekjurnar
• verb eru
• adjective rangar

So the word order is quite regular here.

Yes. You could say:

Því að fjármagnstekjurnar eru rangar, lagfærum við skattstofninn.

If the subordinate clause comes first, the main clause usually shows normal Icelandic verb-second behavior:

• lagfærum við not
• við lagfærum

That kind of word-order change is very common in Icelandic.

Often, yes. Both can mean because.

For example:

• Við lagfærum skattstofninn því að fjármagnstekjurnar eru rangar.
• Við lagfærum skattstofninn af því að fjármagnstekjurnar eru rangar.

Both are natural. There can be differences in style, rhythm, or preference, but for many learners it is enough to know that both commonly mean because.

Possibly, yes, depending on nuance.

• lagfæra often means fix, amend, adjust
• leiðrétta often means correct, rectify

In an administrative or financial context, both may be possible, but they are not always identical in tone. Lagfæra can sound like making an adjustment or fixing something; leiðrétta can sound a bit more directly like correcting an error.

So the original sentence sounds natural, but leiðréttum would also be understandable in many similar contexts.

Yes, it is fairly transparent once you know the parts:

• skattur = tax
• stofn = base / stem / foundation

So skattstofn is literally something like tax base.

This is common in Icelandic: many formal or technical terms are compounds whose parts are easy to recognize once you build up vocabulary.