Learn Hardcore Finnish: Purkki on puolillaan jogurttia, joten syön sen loppuun. - The tub is half full of yogurt, so I eat it up.

puoli = half
adessive plural of puoli → puolilla = on the halves
plus a 3rd-person possessive ending → puolillaan = literally “on its halves”

So Purkki on puolillaan jogurttia is very literally something like:

The jar is at its halves (of capacity) with yogurt.

In actual usage, puolillaan is just a fixed, idiomatic predicate meaning “half full”, especially for containers:

Lasi on puolillaan vettä. – The glass is half full of water.
Kulho on puolillaan sokeria. – The bowl is half full of sugar.

You normally see it in this 3rd‑person form; you don’t usually need to change the possessive ending yourself, you just learn olla puolillaan (jostakin) as a chunk: “to be half full (of something)”.

Why is jogurttia in the partitive case instead of jogurtti?

Jogurttia is the partitive singular of jogurtti.

In this sentence, the partitive is used because:

It’s talking about an indefinite amount of a substance (yogurt), not a clearly bounded, countable item.
With expressions about a container’s contents (täynnä, puolillaan, etc.), Finnish very often uses the partitive for what’s inside.

Typical parallels:

Lasissa on maitoa. – There is (some) milk in the glass.
Pullo on täynnä vettä. – The bottle is full of (some) water.
Kulho on puolillaan riisiä. – The bowl is half full of (some) rice.

Using nominative jogurtti here would sound wrong: it would suggest a single, whole, countable unit called “a yogurt” as such, which doesn’t match the idea of “a jar that is half full of yogurt (as a substance)”.

So:

✅ Purkki on puolillaan jogurttia.
❌ Purkki on puolillaan jogurtti.

Could you also say “Purkki on puoliksi täynnä jogurttia”? Is that the same as “puolillaan jogurttia”?

You can say Purkki on puoliksi täynnä jogurttia, and it is understandable and grammatical. It means roughly the same thing: “The jar is half full of yogurt.”

Nuances:

puolillaan jogurttia
- Very idiomatic and natural with containers + contents.
- Feels like “about half full” as a simple state description.
puoliksi täynnä jogurttia
- More literal: “full to the extent of one half / 50% full”.
- Slightly more explicit about the proportion, and uses the adverb puoliksi (“into a half, to a half degree”).

In everyday speech, puolillaan jogurttia is the more typical phrasing here; puoliksi täynnä is possible but a bit less common in casual talk.

In “joten syön sen loppuun”, what does sen refer to, and why not se or sitä?

Here sen is the object pronoun meaning “it”, and in context it refers to the yogurt (the rest of it in the jar).

Forms of se (“it / that”):

se – nominative (normally a subject)
sen – genitive / total-object form
sitä – partitive object form

Why sen?

syön sen uses sen as a total object: “I will eat it (all of it).”
Adding loppuun reinforces the idea of finishing it completely: “I’ll eat it up / finish it.”

Why not se?

Se is the nominative; you don’t use nominative se as a direct object in this kind of sentence.
- ❌ Syön se – incorrect.
- ✅ Syön sen – correct.

Why not sitä?

sitä is the partitive object: “I eat some of it / I’m (in the process of) eating it, not necessarily to completion.”
Saying syön sitä here would weaken the idea of finishing and would not fit well together with loppuun.

So:

syön sen (loppuun) – I’ll eat it (up / completely).
syön sitä – I’m eating it / I eat it (some amount, with no guarantee of finishing).

What exactly does loppuun mean here, and why is it in the illative case (the -un ending)?

Loppuun is the illative form of the noun loppu = end.

loppu – end
loppuun – into / to the end

In Finnish, a very common pattern is:

verb + noun in illative
→ “do X to the point of Y / until Y is reached”

Here, the pattern is:

syödä loppuun – to eat something until the end, i.e. to finish eating it, to eat it up.

Other examples:

Lukea kirja loppuun. – Read the book to the end / finish the book.
Katsoa elokuva loppuun. – Watch the film to the end.
Juoda kahvi loppuun. – Finish (drinking) the coffee.

So loppuun is literally “to the end” and is in the illative because it expresses reaching a final state.

Is there a difference between “syön sen loppuun” and just “syön sen”?

Both can refer to eating the whole thing, but there’s a nuance:

Syön sen.
- With sen as a total object, this already tends to mean “I’ll eat it (all).”
- It’s neutral; could be about eating it now or in general, depending on context.
Syön sen loppuun.
- Explicitly adds the idea of completion or finishing off the remainder.
- In the context of “Purkki on puolillaan jogurttia”, it suggests:
  - There is some yogurt left (not a full jar anymore).
  - You will finish what remains.

So in English terms, syön sen ≈ “I’ll eat it,” while syön sen loppuun ≈ “I’ll eat it up / I’ll finish it (off).”

Why is the present tense syön used when the English translation is future (“I’ll eat it up”)?

Finnish has no separate future tense. The present tense is used for:

present time: Syön jogurttia. – I am eating yogurt.
generic / habitual: Syön jogurttia usein. – I often eat yogurt.
future: Syön sen myöhemmin. – I’ll eat it later.

Whether syön means “I eat / I am eating” or “I will eat” is decided purely by context and time expressions, not by verb form.

In “Purkki on puolillaan jogurttia, joten syön sen loppuun”, the logical interpretation is future (“so I’ll eat it up now / soon”), because you’re describing a current situation and then an intended response to it.

Could we replace joten with siis or siksi? What’s the difference?

All three can sometimes be translated as “so / therefore”, but they behave a bit differently.

joten
- A conjunction: directly links two clauses as cause → result.
- Very natural here.
- Purkki on puolillaan jogurttia, joten syön sen loppuun.
  – The jar is half full of yogurt, so I’ll eat it up.
siksi
- An adverb meaning “for that reason”.
- Often starts the result clause and may get 2nd position in that clause.
- Purkki on puolillaan jogurttia, siksi syön sen loppuun.
  – The jar is half full of yogurt; for that reason I’ll eat it up.
- Slightly more emphasis on the justification.
siis
- A discourse particle/adverb, like “so / then / in other words”.
- Often marks a conclusion or clarification, sometimes a bit more colloquial or rhetorical.
- Purkki on puolillaan jogurttia, siis syön sen loppuun.
  – The jar is half full of yogurt, so (I conclude) I’ll eat it up.

All three are possible here. Joten is the most neutral, explicitly logical connector; siksi underlines cause–effect; siis sounds a bit more conclusion-like or conversational.

Can the word order be changed, for example to “Purkki on jogurttia puolillaan” or “Sen syön loppuun”?

Finnish word order is flexible, but not all permutations are equally natural.

Purkki on jogurttia puolillaan
- Grammatically possible, but sounds odd in neutral speech.
- The natural, idiomatic order keeps puolillaan right after on and lets the content (jogurttia) follow:
  - Purkki on puolillaan jogurttia.
- You might move jogurttia earlier only for strong emphasis or contrast, but here there’s no real need.
Sen syön loppuun
- This is natural and correct, but has a special emphasis:
  - Sen syön loppuun. – That one I will finish (as opposed to something else).
- Fronting sen (the object) focuses it, often in contrast:
  - Sen syön loppuun, mutta toista purkkia en jaksa.
    – I’ll finish that one, but I don’t have the energy for the other jar.

So:

Neutral: Purkki on puolillaan jogurttia, joten syön sen loppuun.
Emphatic/contrastive: Purkki on puolillaan jogurttia, joten sen syön loppuun.

Does puolillaan always take the partitive like jogurttia here, and what other words behave similarly?

With contents or fill level, puolillaan almost always takes a partitive complement:

Lasi on puolillaan maitoa. – The glass is half full of (some) milk.
Laatikko on puolillaan kirjoja. – The box is half full of books.
Kulho on puolillaan sokeria. – The bowl is half full of sugar.

If the content is countable items, you use partitive plural:

Purkki on puolillaan karkkeja. – The jar is half full of candies.

This pattern is shared by several other “state of fullness” or “covered-with” words:

täynnä – full of
- Pullo on täynnä vettä. – The bottle is full of water.
- Hylly on täynnä kirjoja. – The shelf is full of books.
täpötäynnä – jam-packed with
- Bussi on täpötäynnä ihmisiä.
pullollaan – brimming / full of
- Kaupunki on pullollaan turisteja.

In all of these, the “stuff inside” or “stuff covering” is normally expressed with the partitive.