Learn Hardcore Icelandic: Eftir ráðstefnuna mun hún hafa hitt marga nýja vinnufélaga. - After the conference she will have met many new coworkers.

Icelandic has no single future tense ending like English -will-; instead it uses munu + infinitive.
To make a future perfect (“will have done”), Icelandic uses:

munu + hafa + past participle
Hún mun hafa hitt … = She will have met …

In the whole sentence:

Eftir ráðstefnuna mun hún hafa hitt marga nýja vinnufélaga.
After the conference, she will have met many new colleagues (by that time).

Why is it ráðstefnuna and not ráðstefnan?

Because of definiteness and case.

The base noun is ráðstefna (“conference”), feminine.
The definite form (“the conference”) in the nominative is:
- ráðstefnan = the conference (as subject)
After eftir (“after”), the noun is in the object position of a preposition and here it’s in the accusative:
- ráðstefnuna = the conference (accusative singular, definite)

Mini paradigm (singular):

Nom.: ráðstefnan – the conference (subject)
Acc.: ráðstefnuna – after / for the conference
Dat.: ráðstefnunni
Gen.: ráðstefnunnar

So:
Eftir ráðstefnuna literally: after the conference (accusative, definite).

Which case does eftir take here, and could it also be eftir ráðstefnunni?

In Icelandic, the preposition eftir can govern accusative or dative, depending on meaning and style.

In time expressions like this (after some event), accusative is very common and fully natural:
- eftir ráðstefnuna – after the conference (accusative)
You can also see eftir ráðstefnunni with dative in some styles or contexts. Many speakers accept both, but eftir + accusative is extremely frequent when you mean “after (an event in time)”.

For learning purposes, it’s very safe to memorize expressions like:

eftir sýninguna – after the show
eftir fundinn – after the meeting
eftir ráðstefnuna – after the conference

all with accusative.

Why is the word order Eftir ráðstefnuna mun hún hafa hitt… and not Eftir ráðstefnuna hún mun hafa hitt…?

Icelandic is a verb‑second (V2) language: in a main clause, the finite verb must appear in second position.

In this sentence:

Eftir ráðstefnuna = first element (a fronted adverbial phrase)
The finite verb mun must then come second.
The subject hún must come after the finite verb.

So the correct word order is:

Eftir ráðstefnuna (1) mun (2) hún (3) hafa hitt marga nýja vinnufélaga.

If you start with the subject, you get a different but also correct sentence:

Hún mun hafa hitt marga nýja vinnufélaga eftir ráðstefnuna.

There the subject hún is first, so the finite verb mun is second.

What exactly is the structure of the verb group mun hafa hitt? Why these forms?

The structure is:

mun – finite verb (shows person, number, tense)
- 3rd person singular present of munu (“will, shall”)
hafa – infinitive
- not inflected for person/number here
hitt – past participle / supine of hitta (“to meet”)
- invariant form in this construction

Pattern:

[subject] + mun + hafa + [past participle]

Examples:

Hún mun hafa hitt … – She will have met …
Þeir munu hafa séð … – They will have seen …
Ég mun hafa skrifað … – I will have written …

Only the first verb (mun) is finite and carries person/number; hafa and the participle stay in their fixed forms.

Why is it hitt and not something like hittir or hittur?

Hitt here is the past participle / supine of hitta.

When you use hafa (“to have”) as an auxiliary to form perfect or future perfect tenses, the past participle does not agree with the subject (or object) in gender and number. It appears in a neutral, invariant form (often called the supine).

So you say:

Ég hef hitt hana. – I have met her.
Þú hefur hitt hana. – You have met her.
Við höfum hitt hana. – We have met her.
Hún mun hafa hitt hana. – She will have met her.

It’s always hitt after hafa, never hittur, hittir, etc.

Forms like hittur would appear only if hitta were used as an adjective-like participle agreeing with a noun (e.g. with vera: dyrnar eru opnar / hurðin er lokuð), but hitta doesn’t really form a common adjective in that way.

Why are marga and nýja in those forms, and how do they relate to vinnufélaga?

Marga (“many”) and nýja (“new”) are adjectival words that must agree with the noun vinnufélaga in:

Gender: masculine
Number: plural
Case: accusative (as the object of “hafa hitt”)

Breakdown:

Base form: margur (many) – masculine adjective/pronoun
- Accusative plural masculine: marga
Base form: nýr (new) – masculine adjective
- Accusative plural masculine: nýja
Noun: vinnufélagi (coworker, colleague), masculine
- Accusative plural: vinnufélaga

So the whole noun phrase in accusative plural masculine is:

marga nýja vinnufélaga – many new colleagues

If it were the subject instead (nominative plural), you’d see:

margir nýir vinnufélagar – many new colleagues (subject form)

Why is it vinnufélaga and not vinnufélagar?

Because vinnufélaga here is in the accusative plural, not the nominative.

The noun vinnufélagi (“coworker, colleague”) is masculine; its plural looks roughly like this:

Nom. pl.: vinnufélagar – colleagues (as subject)
Acc. pl.: vinnufélaga – colleagues (as object)
Dat. pl.: vinnufélögum
Gen. pl.: vinnufélaga

In the sentence, marga nýja vinnufélaga is the direct object of hafa hitt, so it must be accusative plural:

Hún mun hafa hitt marga nýja vinnufélaga.
She will have met many new colleagues.

If they were the subject, you’d say:

Margir nýir vinnufélagar munu mæta.
Many new colleagues will attend.

Why is there no definite article in marga nýja vinnufélaga?

Because the phrase is indefinite, like English “many new colleagues”, not “the new colleagues”.

Icelandic usually marks definiteness by a suffix on the noun:
- vinnufélagar – colleagues
- vinnufélagarnir – the colleagues
You don’t combine “marga” (many) with a suffixed definite article in this simple way; “many new colleagues” is naturally interpreted as indefinite.

So:

marga nýja vinnufélaga = many new colleagues (indefinite)
hinir mörgu nýju vinnufélagar = the many new colleagues (more marked, with a separate article hinir
- nominative)

If you wanted to say “many of her new colleagues”, you might say:

marga nýja vinnufélaga hennar – many new colleagues of hers
marga af nýjum vinnufélögum hennar – many of her new colleagues

Can I move eftir ráðstefnuna to another place in the sentence?

Yes. The phrase eftir ráðstefnuna is an adverbial (time expression), and Icelandic allows some flexibility in its position, as long as the finite verb stays in second position.

Possible variants:

Eftir ráðstefnuna mun hún hafa hitt marga nýja vinnufélaga.
(Time phrase first; verb mun second.)
Hún mun hafa hitt marga nýja vinnufélaga eftir ráðstefnuna.
(Subject first; time phrase later.)
With extra emphasis you might see commas in writing:
Hún mun, eftir ráðstefnuna, hafa hitt marga nýja vinnufélaga.

All of these are grammatical; the difference is mostly in emphasis and style, not in basic meaning.

What is the difference between mun hún hafa hitt and mun hún hitta in this context?

The difference is the same as in English between:

She will meet … (simple future)
She will have met … (future perfect)

In Icelandic:

Mun hún hitta – she will meet
- A simple future action in the future.
- Example:
  Eftir ráðstefnuna mun hún hitta marga nýja vinnufélaga.
  After the conference she will meet many new colleagues (perhaps at a new job that starts then).
Mun hún hafa hitt – she will have met
- A completed action before some future reference point.
- In the given sentence, the idea is: > By the time the conference is over, she will already have met many new colleagues.

So “mun hún hafa hitt” implies the meeting happens up to that future point (during the conference), whereas “mun hún hitta” suggests the meeting happens after that point.

How would I make the sentence negative, and where does ekki go?

The basic rule: in main clauses, ekki (“not”) generally comes right after the finite verb.

Finite verb here: mun. So the negative sentence is:

Eftir ráðstefnuna mun hún ekki hafa hitt marga nýja vinnufélaga.
After the conference, she will not have met many new colleagues.

Or with subject first:

Hún mun ekki hafa hitt marga nýja vinnufélaga eftir ráðstefnuna.

Note:

mun = finite verb (stays in 2nd position)
ekki = placed immediately after mun.