Við greinum tvo liti.

Because greinum is the 1st person plural present tense form of the verb greina.

• að greina = to distinguish / to analyze
• við greinum = we distinguish / we analyze

So the ending -um tells you the subject is we.

A quick comparison:

• ég greini = I distinguish
• þú greinir = you distinguish
• við greinum = we distinguish

The base form is að greina.

In dictionaries, Icelandic verbs are normally listed in the infinitive with að:

• að greina = to distinguish

From that, you get forms like:

• greini
• greinir
• greinum

So if you want to look up greinum, look for greina.

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

The verb greina takes a direct object, and direct objects in Icelandic are often in the accusative. Here, two colors is the object, so both the number and the noun must be in accusative plural.

• nominative: tveir litir = two colors
• accusative: tvo liti = two colors

So in this sentence:

• Við = subject
• greinum = verb
• tvo liti = direct object in the accusative

Yes. Litur is masculine, and that affects both the noun form and the form of the number two.

Some key forms are:

• singular nominative: litur
• plural nominative: litir
• plural accusative: liti

Because litur is masculine, two appears as:

• tveir in nominative plural
• tvo in accusative plural

If the noun were a different gender, the form of two would be different.

In Icelandic, numbers can change for gender, case, and sometimes number agreement.

For two, the common forms are:

• masculine nominative: tveir
• masculine accusative: tvo
• feminine nominative/accusative: tvær
• neuter nominative/accusative: tvö

So tvo liti tells you:

• the noun is masculine
• the phrase is in the accusative

This is one of the things that makes Icelandic feel very grammatical compared with English.

Yes, greinum already shows 1st person plural, so technically the verb form itself tells you the subject is we.

But Icelandic normally does use subject pronouns in ordinary sentences:

• Við greinum tvo liti.

Leaving out við would usually sound unusual or incomplete in normal modern Icelandic unless the context makes it very clear.

So unlike some languages where subject pronouns are often dropped, Icelandic usually keeps them.

Yes. Greina is a useful verb with several related meanings, including:

• distinguish
• identify
• analyze
• sometimes detect

So depending on context, Við greinum tvo liti could be understood as something like:

• we distinguish two colors
• we can tell two colors apart
• we identify two colors

The exact English translation depends on the context, but the grammar stays the same.

A simple learner-friendly approximation is:

Vith GRAY-num TVOH LIH-tih

A few notes:

• ð in Við is like the th in this
• í is a long ee sound
• ei in greinum sounds roughly like ay
• tv at the start of tvo can feel tricky for English speakers
• i in liti is a short i, like bit

A more careful pronunciation will vary by speaker and accent, but that approximation is a good start.

Because the sentence is talking about two colors in an indefinite way, not the two colors.

Icelandic does have a definite article, but it is usually attached to the end of the noun rather than written as a separate word.

Compare:

• liti = colors
• litina = the colors

So:

• tvo liti = two colors
• tvo litina = the two colors

Yes, Icelandic word order is somewhat flexible, but the normal neutral order here is:

• Við greinum tvo liti.

That is:

• subject + verb + object

Because Icelandic marks case, other orders are sometimes possible for emphasis or style. But for a learner, this sentence is best understood as the standard, straightforward order.

So this is the safest pattern to copy at first.

Knowing the forms helps you recognize why liti appears in this sentence.

Here are the main forms of litur:

Singular

• nominative: litur
• accusative: lit
• dative: lit
• genitive: litar

Plural

• nominative: litir
• accusative: liti
• dative: litum
• genitive: lita

In Við greinum tvo liti, the object is plural accusative, so you get:

• tvo
  • liti

This is a very common Icelandic pattern: the adjective/number and the noun both reflect the required case.

Yes, they would.

For one color, you would use the singular accusative of the noun:

• Við greinum einn lit.

For three colors, you would use the plural accusative:

• Við greinum þrjá liti.

So the object changes depending on the number, and the number word also has to match the noun’s gender and case.

That is why Icelandic learners spend so much time on declension: even simple phrases like two colors require agreement.