Learn Hardcore Finnish: Minä menen kotiin seminaarin jälkeen.

The -in ending here is the illative ending meaning movement into or to a place.
Because the verb mennä (to go) expresses movement towards somewhere, the destination takes the illative:

Menen kotiin. = I go home / I’m going home.
Olen kotona. = I am at home. (different case: adessive)

So in this sentence, kotiin is required to express “to home,” not just koti.

Both kotiin and seminaariN end in -n. Are they the same case?

No, they are two different things that just happen to both end in -n in the written form.

kotiin
- Base form: koti
- Case: illative (movement into)
- Ending: -in (a two-letter ending, not just -n)
- Meaning: “to home”
seminaariN
- Base form: seminaari
- Case: genitive (often used for possession and required by some postpositions)
- Ending: -n
- Meaning: “of the seminar,” but here it’s just the form needed before jälkeen

So:

koti + in → kotiin (illative)
seminaari + n → seminaarin (genitive)

They look similar, but grammatically they are different cases with different functions.

Why is it seminaariN jälkeen, not seminaari jälkeen?

Because the word jälkeen (after) is a postposition that requires the noun before it to be in the genitive case.

Base form: seminaari (seminar)
Genitive: seminaari + n → seminaarin

Structure:

seminaariN jälkeen = after the seminar

This is a fixed pattern: [GENITIVE] + jälkeen
Some other examples:

työn jälkeen = after work
loman jälkeen = after the holiday
kokouksen jälkeen = after the meeting

So seminaari jälkeen is ungrammatical; it must be seminaarin jälkeen.

Why is jälkeen placed after the noun instead of before it, like English “after the seminar”?

Finnish often uses postpositions, which come after the noun, instead of prepositions that come before it.

Pattern:

English: after the seminar
Finnish: the seminar + after → seminaariN jälkeen

More examples of postpositions:

talon edessä = in front of the house
talon takana = behind the house
talon lähellä = near the house

In all these, the structure is:

[noun in genitive] + [postposition]

So jälkeen behaves like those: it’s a postposition that follows the noun and takes genitive.

Can I leave out minä and just say Menen kotiin seminaarin jälkeen?

Yes. In normal Finnish you will very often drop the pronoun:

Menen kotiin seminaarin jälkeen.

This is fully natural and usually preferred in everyday speech and writing.
The subject is clear from the verb ending:

menen = I go
menet = you (sg.) go
hän menee = he/she goes
menemme = we go
menette = you (pl.) go
he menevät = they go

You generally use minä when you want to:

emphasize the subject (Minä menen, en sinä. = I am going, not you.)
contrast different people

But grammatically, the sentence works perfectly fine without minä.

Does minä menen mean “I go”, “I am going” or “I will go”?

The Finnish present tense covers all of these English meanings, depending on context:

I go
I am going
I will go / I’m going to go

In Minä menen kotiin seminaarin jälkeen, the most natural translation is:

I’m going home after the seminar. or
I will go home after the seminar.

There is no separate continuous form (am going) in Finnish, and there is no special future tense either. Context and time expressions (like huomenna, jälkeen, ensi viikolla) tell you if the action is future, present, or habitual.

Is the word order fixed? Can I also say Minä menen seminaarin jälkeen kotiin or Seminaarin jälkeen menen kotiin?

All of these are grammatically correct; the differences are about emphasis and flow, not basic meaning.

Acceptable variants:

Minä menen kotiin seminaarin jälkeen.
- Neutral, common: focus slightly on going home.
Minä menen seminaarin jälkeen kotiin.
- Also correct; slightly stronger focus on the time (“after the seminar”) before giving the destination.
Menen kotiin seminaarin jälkeen.
- Same as (1), but without minä; very natural.
Seminaarin jälkeen menen kotiin.
- The time expression is at the beginning, so you’re emphasizing when it happens:
  “As for after the seminar, that’s when I go home.”

Finnish word order is quite flexible, but:

The verb usually comes early (often second in the clause).
You can move elements to the beginning to highlight or contrast them.

Could I say Minä lähden kotiin seminaarin jälkeen instead of Menen kotiin? What’s the difference?

You can say that, and it’s natural, but there is a nuance difference:

mennä = to go (neutral movement from A to B)
- Menen kotiin. = I go / am going home.
lähteä = to leave, to set off
- Lähden kotiin. = I leave for home / I set off home (emphasizes the starting to leave)

In many contexts, both are possible:

After the seminar, you both leave the venue and go home, so both verbs fit.

However:

If you stress the moment of departure: Lähden kotiin kello viisi.
If you stress the journey/destination: Menen kotiin bussilla.

Your original sentence with mennä is neutral and very common.

What’s the difference between koti, kotiin, kotona, kodissa, and kotoa?

They are different cases of the word koti (“home”), each expressing a different relation to the place.

Most common ones:

koti (nominative)
- Base form, used mostly in dictionary/subject roles.
- Example: Koti on kaukana. = Home is far away.
kotiin (illative) – to home / into home
- Movement to the inside of home.
- Menen kotiin. = I go (am going) home.
kotona (adessive) – at home (colloquial meaning “at home”)
- Location, “being at home”.
- Olen kotona. = I am at home.
kodissa (inessive) – in the home, inside the home
- More literal “inside the home/house” (less idiomatic than kotona when you just mean at home).
- Siinä kodissa on kolme makuuhuonetta. = In that home there are three bedrooms.
kotoa (elative) – from (one’s) home
- Movement from home.
- Lähden kotoa kello kahdeksan. = I leave home at eight.

In your sentence, you need movement to, so you use kotiin.

Why does jälkeen use the genitive (seminaariN), while from in English would be another preposition (from the seminar)? Could we say something like seminaariSTA kotiin?

jälkeen and endings like -sta express different relationships:

seminaariN jälkeen (after the seminar)
- jälkeen = after
- Requires genitive: seminaariN
- Emphasizes time: action happens after the event has ended.
seminaariSTA kotiin (from the seminar (location) to home)
- -sta (elative) = from inside/out of
- Emphasizes place: movement from the place of the seminar.
- Example sentence: Menen seminaarista kotiin. = I go home from the seminar.

So:

seminaariN jälkeen = after the seminar (time)
seminaariSTA kotiin = from the seminar (to) home (place)

They are both correct Finnish, but they mean different things and are not interchangeable. Your sentence is about time: you go home after the seminar has finished, not necessarily directly from the seminar venue.

Is seminaari treated like a normal Finnish word even though it looks international?

Yes. Loanwords like seminaari are fully integrated into Finnish declension patterns.

Nominative: seminaari (seminar)
Genitive: seminaariN → seminaarin
Partitive: seminaariA → seminaaria
Inessive (in): seminaariSSA → seminaarissa
Elative (out of, from inside): seminaariSTA → seminaarista
Illative (into): seminaariIN → seminaariin

So in seminaariN jälkeen, seminaariN is just the regular genitive of seminaari, required by the postposition jälkeen.