Kurteisin skiptir máli í góðu samtali.

Kurteisin is kurteisi with the suffixed definite article -in, so literally it is the politeness.

A few useful points:

• kurteisi = politeness, courtesy
• kurteisin = the politeness

In Icelandic, the definite article is usually attached to the end of the noun instead of being a separate word like English the.

Also, Icelandic and English do not always use definiteness in exactly the same way. So even though kurteisin is literally the politeness, natural English may still just say politeness.

Kurteisin is in the nominative singular, because it is the subject of the sentence.

The sentence structure is:

• Kurteisin = the subject
• skiptir máli = matters / makes a difference
• í góðu samtali = in a good conversation

So the thing that matters is kurteisin, and subjects are normally in the nominative.

skipta máli is a very common Icelandic expression meaning:

• to matter
• to make a difference
• to be important

So in this sentence, skiptir máli should be understood as one unit.

Word by word, it may not feel very transparent to an English speaker, so it is best to learn skipta máli as a fixed expression.

Skiptir is the 3rd person singular present form of the verb skipta.

That matches the subject kurteisin, which is singular.

So:

• að skipta = to matter / to make a difference
• skiptir = matters

Compare:

• Þetta skiptir máli. = This matters.
• Kurteisin skiptir máli. = Politeness matters.

Because the expression is skipta máli, and in that expression mál appears in the dative singular: máli.

So this is something you largely need to learn with the phrase itself:

• mál = matter, issue
• máli = dative singular of mál
• skipta máli = to matter

This is very common in Icelandic: a verb or expression often requires a specific case, and that case does not always match what an English speaker would expect.

There are two things going on here:

1. í can take different cases

   • dative for location/state
   • accusative for motion into something

2. Here the meaning is in the sense of within a conversation / in the context of a conversation, so Icelandic uses the dative.

That gives:

• samtal = conversation
• samtali = dative singular

And the adjective has to match:

• góður = good
• góðu = dative singular neuter

So:

• í góðu samtali = in a good conversation

Because it agrees with samtali.

The noun samtal is:

• neuter
• singular
• dative here, because of í

So the adjective must also be:

• neuter
• singular
• dative

That produces góðu.

This kind of agreement is one of the biggest differences from English: in Icelandic, adjectives change form to match the noun’s gender, number, and case.

Because Icelandic usually puts the definite article onto the noun itself rather than using a separate word.

So instead of an English-style pattern like the conversation, Icelandic often has a noun ending that carries the meaning of the.

In this sentence, though, samtali is indefinite:

• í góðu samtali = in a good conversation

So there is no definite article there.

Yes. Very often, that is the most natural English translation.

Even though kurteisin is formally definite, English may prefer a bare abstract noun:

• Kurteisin skiptir máli
  natural English: Politeness matters

This is a good reminder that you should not always translate Icelandic definiteness mechanically word for word.

Yes. Icelandic has a strong verb-second tendency in main clauses.

In the original sentence:

• Kurteisin = first element
• skiptir = second element

You could also front the prepositional phrase for emphasis:

• Í góðu samtali skiptir kurteisin máli.

That still keeps the finite verb skiptir in second position.

So word order can change, but the verb usually stays in the second slot in a main clause.

Here are the main forms to learn:

• kurteisi — noun, feminine
• skipta — verb
• mál — noun, neuter
• samtal — noun, neuter
• góður — adjective

And here are the exact forms used in the sentence:

• kurteisin = nominative singular definite of kurteisi
• skiptir = 3rd person singular present of skipta
• máli = dative singular of mál
• góðu = dative singular neuter of góður
• samtali = dative singular of samtal

Learning both the dictionary form and the form used in the sentence is especially helpful in Icelandic, because endings carry so much grammatical information.