Kennarinn segir að framtíðin í þessari setningu sé ekki rétt.

In Icelandic, the definite article is usually attached to the end of the noun.

• kennari = teacher
• kennarinn = the teacher

So -inn here is the masculine singular definite article.

This is very different from English, where the is a separate word.

Segir is the 3rd person singular present tense of segja = to say.

It is used because the subject is Kennarinn = the teacher, which is singular.

A few useful forms:

• ég segi = I say
• þú segir = you say
• hann/hún segir = he/she says

So Kennarinn segir means The teacher says.

Here að means that and introduces a subordinate clause:

• Kennarinn segir að ...
• The teacher says that ...

English often drops that, but Icelandic usually keeps að in this kind of sentence.

So the structure is:

• main clause: Kennarinn segir
• subordinate clause: að framtíðin í þessari setningu sé ekki rétt

Sé is the present subjunctive of vera = to be.

This is a very common thing learners notice. After verbs like segja when reporting someone’s opinion, judgment, or statement, Icelandic often uses the subjunctive in the subordinate clause.

So:

• er = indicative, plain is
• sé = subjunctive be / is in a reported or less directly asserted statement

In this sentence, sé shows that this is the teacher’s assessment: the teacher says it is not correct.

Very roughly:

• segir að ... er = more direct/plain statement
• segir að ... sé = reported judgment/opinion style

Here framtíðin does not mean just the future in a general time sense. In this grammar context, it means the future tense or the future form.

So in this sentence, framtíðin is being used as a grammatical term.

• framtíð = future / future tense
• framtíðin = the future / the future tense

Because the sentence is talking about grammar inside a sentence, the meaning is clearly the future tense.

Because í here means in in the sense of location, it takes the dative case.

That is why you get:

• þessari = dative singular feminine of þessi = this
• setningu = dative singular of setning = sentence

So:

• þessi setning = this sentence
• í þessari setningu = in this sentence

A useful rule:

• í + dative = in, inside, located in
• í + accusative can be used when there is motion into something

Because it is in the dative singular after í.

The basic form is:

• setning = sentence

But after í with a location meaning, it changes to:

• í setningu = in a sentence
• í þessari setningu = in this sentence

Many feminine nouns of this type take -u in the dative singular, so this is a pattern worth getting used to.

Because ekki negates the predicate rétt.

The pattern is:

• sé ekki rétt = is not correct

In Icelandic, ekki usually comes after the finite verb and before the adjective or phrase being negated.

So here:

• sé = is / be
• ekki = not
• rétt = correct

Together: sé ekki rétt = is not correct

A little, yes, but the given order is natural.

In framtíðin í þessari setningu, the phrase í þessari setningu belongs closely with framtíðin and tells you which future tense use is being discussed: the one in this sentence.

So the sentence naturally groups like this:

• Kennarinn segir
• að [framtíðin í þessari setningu] sé ekki rétt

If you move í þessari setningu elsewhere, the emphasis can change, and in some cases the sentence may sound less natural or mean something slightly different. So for learners, the given order is a good model to follow.