Learn Hardcore Finnish: Viikonlopun seminaarissa on monta puhujaa ja yksi puheenjohtaja. - At the weekend seminar there are many speakers and one chairperson.

Viikonlopun is the genitive singular of viikonloppu (weekend), and here it functions like an attributive/possessive modifier: the weekend’s seminar or the seminar of the weekend → the weekend seminar.

viikonloppu = weekend (basic / nominative form)
viikonlopun = of the weekend / weekend’s (genitive)

Finnish often uses the genitive in front of a noun to express what English would show with another noun or an 's:

koulun piha = the school’s yard / the school yard
viikonlopun seminaari = the weekend’s seminar / the weekend seminar

So viikonlopun seminaarissa literally: in the weekend’s seminar.

What does the ending -ssa in seminaARISSA mean?

The ending -ssa/-ssä is the inessive case, which usually corresponds to English in or at.

seminaari = seminar
seminaari-ssa = in/at the seminar

You use -ssa/-ssä not only for physical locations but also for events and situations:

kokouksessa = at the meeting
juhlissa = at the party / parties
kurssilla (this is -lla, another case) = on the course

So viikonlopun seminaarissa = at the weekend seminar.

Why is the verb on used here, and how should I understand this structure?

This is a typical existential sentence in Finnish, used to say there is / there are somewhere.

Structure:

[Location] + on + [thing(s) that exist there]

So:

Viikonlopun seminaarissa = at the weekend seminar (location)
on = there is / there are
monta puhujaa ja yksi puheenjohtaja = many speakers and one chairperson

A more literal English rendering is:

At the weekend seminar there is/are many speakers and one chairperson.

So on here means there is / there are, even though it is grammatically a 3rd person singular verb.

Why is it on (singular) and not ovat (plural) when we have many speakers?

In Finnish existential sentences, the verb is almost always 3rd person singular on, even if the logical subject is plural or contains multiple items:

Pöydällä on kirjoja. = There are books on the table.
Huoneessa on kaksi ihmistä. = There are two people in the room.

Your sentence fits the same pattern:

Viikonlopun seminaarissa on monta puhujaa ja yksi puheenjohtaja.

If you used a clearly definite plural subject in the nominative, you could have ovat:

Puhujat ovat seminaarissa. = The speakers are at the seminar.

But with existential there is/are sentences, Finnish prefers on.

Why do we say monta puhujaa and not monta puhuja or monta puhujia?

The pattern is:

monta
- partitive singular of the noun.

Puhuja → partitive singular is puhujaa, so:

monta puhujaa = many speakers

A few key points:

monta itself is the partitive form of moni (many).
After monta, the noun is in partitive singular, even though the meaning is plural:
- monta koiraa = many dogs
- monta kirjaa = many books
- monta puhujaa = many speakers

Forms like monta puhuja or monta puhujia are ungrammatical.

What case is puhujaa, and why is it used here?

Puhujaa is partitive singular of puhuja (speaker).

puhuja = speaker (nominative)
puhujaa = speaker (partitive singular)

It appears in the partitive singular because of the quantifier monta. As mentioned, monta always requires the partitive singular:

monta opiskelijaa = many students
monta kysymystä = many questions
monta puhujaa = many speakers

Why is it yksi puheenjohtaja (nominative) and not yhtä puheenjohtajaa (partitive)?

With the number yksi (one), the following noun is normally in the nominative singular:

yksi puheenjohtaja = one chairperson
yksi kirja = one book
yksi puhuja = one speaker

The partitive form yhtä puheenjohtajaa exists, but it’s used in contexts where the whole phrase is in the partitive case, often with certain verbs or to express incompleteness, negation, or emphasis:

En nähnyt yhtäkään puheenjohtajaa. = I didn’t see even one chairperson.
Tarvitsisimme yhtä puheenjohtajaa lisää. = We would need one more chairperson.

In a simple existential positive statement like yours, the default is:

on yksi puheenjohtaja = there is one chairperson.

How do other numbers behave with nouns, compared to yksi?

Pattern:

yksi
- nominative singular
kaksi, kolme, neljä, ..., and quantifiers like monta, paljon
- partitive singular

Examples:

yksi puheenjohtaja = one chairperson (nominative singular)
kaksi puheenjohtajaa = two chairpersons (partitive singular)
kolme puhujaa = three speakers (partitive singular)
paljon puhujia = many/a lot of speakers (usually partitive plural here)
monta puhujaa = many speakers (partitive singular)

So your sentence is perfectly regular:

monta puhujaa (many speakers)
yksi puheenjohtaja (one chairperson)

What is the difference between monta puhujaa and something like paljon puhujia?

Both can often be translated as many speakers, but there are nuances:

monta puhujaa
- Strictly countable number of individuals
- Structure: monta
  - partitive singular
- Slightly more count-focused feeling.
paljon puhujia
- More general a lot of speakers, often with mass/amount nuance
- Structure: paljon
  - partitive plural

In practice, they frequently overlap and both sound natural in this sentence:

Viikonlopun seminaarissa on monta puhujaa.
Viikonlopun seminaarissa on paljon puhujia.

Both: There are many/a lot of speakers at the weekend seminar.

What is the difference in meaning between puhuja and puheenjohtaja?

puhuja = speaker (anyone who gives a talk, presentation, or speech)
puheenjohtaja = chairperson, literally leader of the speech/meeting

Typical roles in a seminar:

puhuja(t) give presentations or talks.
puheenjohtaja chairs or moderates the session: opens it, introduces speakers, keeps time, leads discussion, etc.

So the sentence says there are many people giving talks and one person chairing the event/session.

How is the word puheenjohtaja formed, and why is it not inflected inside?

Puheenjohtaja is a compound word:

puheen = genitive of puhe (speech) → of speech / of the talk
johtaja = leader, director

So puheenjohtaja ≈ leader of the speech/meeting → chairperson.

When Finnish makes a compound like this, the first part stays in a fixed form (here genitive puheen) and only the whole compound is inflected:

nominative: puheenjohtaja
genitive: puheenjohtajan
inessive: puheenjohtajassa, etc.

In your sentence, after yksi, it is in plain nominative singular: yksi puheenjohtaja.

Could the word order be different, for example Monta puhujaa ja yksi puheenjohtaja on viikonlopun seminaarissa?

Yes, that word order is grammatically possible, but the focus changes.

Viikonlopun seminaarissa on monta puhujaa ja yksi puheenjohtaja.
- Neutral existential: talks first about the place/event, then says what exists there.
- Natural equivalent of At the weekend seminar, there are many speakers and one chairperson.
Monta puhujaa ja yksi puheenjohtaja on viikonlopun seminaarissa.
- Now you first mention who/what you’re talking about, then where they are.
- Closer to Many speakers and one chairperson are at the weekend seminar.

Both are allowed; the first one is more typical when introducing what a place/event consists of.

Why doesn’t Finnish use a separate word for in/at like English does?

Finnish expresses many relations that English uses prepositions for by using case endings instead.

Instead of:

in the seminar
at the seminar

Finnish attaches case endings to the noun:

seminaari
- -ssa → seminaARISSA = in/at the seminar
pöytä
- -llä → pöydällä = on the table
kaupunki
- -ssa → kaupungissa = in the city

So separate prepositions are much rarer in Finnish; case endings mostly do that job.

There are no words like a or the here. How do we know if it means many speakers and one chairperson or the many speakers and the one chairperson?

Finnish has no articles (a/an, the). Definite vs. indefinite meaning is understood from:

Context
Word order and emphasis
Sometimes pronouns or other modifiers

Your sentence:

Viikonlopun seminaarissa on monta puhujaa ja yksi puheenjohtaja.

In normal context, this naturally means:

There are many speakers and one chairperson at the weekend seminar.
(indefinite: we are just stating what the seminar has)

If you wanted to emphasize definiteness, you’d use context or specify more:

Viikonlopun seminaarissa ovat ne monet puhujat ja se yksi puheenjohtaja.
= At the weekend seminar (there) are those many speakers and that one chairperson.

But in everyday usage, the original sentence is taken as indefinite unless context clearly makes it specific.