Learn Hardcore Finnish: Koira on pöydän alla, kun perhe istuu sen ääressä. - The dog is under the table when the family sits at it.

In Finnish, many location words like alla (under), päällä (on top of), takana (behind) are postpositions: they come after the noun and require the noun to be in the genitive case.

pöytä = table (nominative)
pöydän = of the table (genitive)
alla = under

So the structure is literally: “under of-the-table” → pöydän alla.

Using nominative pöytä alla would be grammatically wrong here, because alla specifically demands the genitive form of the noun it relates to.

What is alla exactly? Is it a preposition or some kind of case ending?

alla is a postposition, not a case ending.

A preposition would come before the noun (like English “under the table”).
A postposition comes after the noun: pöydän alla (“under the table”).

In form, alla looks like an adessive case form (the -lla/llä ending), and historically it’s related, but in modern grammar it’s treated as an independent word that governs the genitive:

pöydän alla = under the table
talon takana = behind the house
oven edessä = in front of the door

So the pattern is: [noun in genitive] + [postposition].

What’s the difference between alla, alhaalla, and alle?

All three relate to “under/below”, but they do different jobs:

alla – static location under something (where?):
- Koira on pöydän alla. – The dog is under the table.
alhaalla – “down, in a low place / down below” (more general, not tied to a specific object):
- Koira on alhaalla. – The dog is down (below, downstairs, etc.).
  It doesn’t specify “under the table” or “under the bed”; just “down, below”.
alle – movement to a position under something (where to?):
- Koira menee pöydän alle. – The dog goes under the table.

So:

alla = under (static)
alle = under (movement to that place)
alhaalla = down / below (general low-position location)

Why is there a comma before kun? Is it required?

Yes, in standard written Finnish you normally put a comma before kun when it introduces a subordinate clause.

The structure is:

Main clause: Koira on pöydän alla
Subordinate clause introduced by kun: kun perhe istuu sen ääressä.

Rule of thumb:
If kun (or että, koska, vaikka, jos, etc.) introduces a full clause with its own verb, that clause is set off with a comma:

Nukun, kun olen väsynyt. – I sleep when I’m tired.
Lähdemme, kun sade loppuu. – We’ll leave when the rain stops.

Spoken Finnish may ignore commas, but in writing, the comma before kun is standard here.

What does kun mean here, and how is it different from koska?

In this sentence, kun is temporal and means “when”:

…kun perhe istuu sen ääressä.
→ “…when the family sits at it.”

kun can mean both “when” and sometimes “because”, depending on context.
koska is more clearly “because” and is less ambiguous.

Compare:

Koira on pöydän alla, kun perhe istuu sen ääressä.
= When the family is sitting at the table, the dog is under it. (time)
Koira on pöydän alla, koska perhe istuu sen ääressä.
= The dog is under the table because the family is sitting at it. (reason)

So here kun focuses on time (“at the time when”), not on cause.

Can I change the word order to: Kun perhe istuu sen ääressä, koira on pöydän alla?

Yes, that’s perfectly correct and actually very natural.

Finnish is quite flexible with word order, especially with main + subordinate clauses. Both are fine:

Koira on pöydän alla, kun perhe istuu sen ääressä.
Kun perhe istuu sen ääressä, koira on pöydän alla.

The difference is one of emphasis and focus:

Starting with Koira on pöydän alla makes the dog’s location the starting point.
Starting with Kun perhe istuu… foregrounds the time / situation, like English “When the family is sitting at the table, the dog is under it.”

What does ääressä literally mean, and why do we say sen ääressä instead of something like pöydällä?

ääressä is the adessive form of ääri (“edge, border”).
Literally, jonkin ääressä is “at the edge of something”, “by something”, “at something”.

In practice, pöydän ääressä is an idiomatic way to say “at the table”, especially in the sense of sitting there to eat, work, talk, etc.

Contrast:

pöydällä = on the table (on its surface)
pöydän ääressä = at the table (sitting by it, at its edge)

In your sentence, sen ääressä = “at it” (at its edge → at the table). Using pöydällä would give a different image, like the family physically sitting on top of the table.

What is sen referring to in sen ääressä, and why is it sen and not se?

sen here refers to pöytä (“the table”), mentioned just before.

se = it (nominative)
sen = of it / its (genitive)

The pattern [noun/pronoun in genitive] + ääressä means “at [something]”. Because ääressä behaves like a postposition semantically, it takes the genitive:

pöydän ääressä = at the table
sen ääressä = at it (at the table)

So sen is used because ääressä requires the genitive form of the pronoun. Using se ääressä would be wrong in standard Finnish.

Why is it perhe istuu (singular verb) if perhe means “family” (a group of people)?

In Finnish, perhe is grammatically singular, even though it refers to a group:

perhe = (a) family
perheet = (the) families

Verbs agree with the grammatical number, not with the “real-world” number of people inside the group. So we say:

Perhe istuu pöydän ääressä. – The family is sitting at the table.
Perheet istuvat pöydän ääressä. – The families are sitting at the table.

This is different from English only in appearance; English also usually uses singular with “family” in British-style usage (“The family is sitting…”), though American English often allows plural (“The family are…”). In Finnish, only the singular verb is correct with singular perhe.

Could we say pöytänsä ääressä instead of sen ääressä? What would be the difference?

Yes, you could say:

…kun perhe istuu pöytänsä ääressä.

pöytänsä consists of:

pöytä = table
pöydä- = stem
pöytän- (genitive-like base)
-sä = 3rd-person possessive suffix (his/her/its/their)

So pöytänsä = “their/its table”.

Difference in nuance:

sen ääressä = “at its edge / at it” referring back to that table just mentioned (anaphoric “it”).
pöytänsä ääressä = “at their table”, explicitly marking possession (the table that belongs to the family).

Your original sentence focuses more on the situation (“at it”) than on ownership; pöytänsä ääressä would slightly underline that it’s the family’s own table.

Why are there no words for “the” or “a” before koira and pöytä? How do I know if it means “a dog” or “the dog”?

Finnish has no articles (no “a/an” or “the”). Nouns like koira and pöytä can correspond to English “a dog / the dog”, “a table / the table”, depending on context.

Koira on pöydän alla.
Could be “The dog is under the table” or “A dog is under the table.”

How do you know?

If something has been mentioned or is assumed to be known, English would usually use “the”, but Finnish just repeats the plain noun.
If you introduce something new, English uses “a”, but Finnish still just uses the plain noun.

Context of the conversation or text decides whether you translate with a/an or the in English; the Finnish form does not change.

What kind of time meaning does kun perhe istuu have? Is it “whenever the family sits” or “while the family is sitting”?

kun + present tense verb is flexible and can cover both:

Specific time / situation (like “while / when (right now)”):
- Koira on pöydän alla, kun perhe istuu sen ääressä.
  → The dog is under the table when/while the family is sitting at it (in that situation).
General, habitual time (“whenever, every time”):
Depending on context, the same Finnish sentence can also imply:
→ Whenever the family sits at the table, the dog is under it.

If you want to emphasize habitual/whenever, you can make it clearer with adverbs like aina:

Koira on aina pöydän alla, kun perhe istuu sen ääressä.
= The dog is always under the table when(ever) the family sits at it.

So the base sentence is compatible with both a specific and a habitual reading; the context decides which feels more natural.