Learn Hardcore Finnish: Aikuinen juo teetä keittiössä.

Because the object is an indefinite amount of a mass noun. With verbs like juoda (to drink) and syödä (to eat), Finnish typically uses the partitive for unbounded/indefinite quantity (some tea, tea in general) or ongoing action. So teetä signals “some tea” rather than a specific, bounded portion.

Could I say Aikuinen juo teen? What would that mean?

Yes. Teen (genitive singular) is a total object. Aikuinen juo teen implies a specific tea and that the action is bounded/completed (the adult drinks the tea, all of it). Compare:

Aikuinen juo teetä = drinks some tea / tea in general (unbounded).
Aikuinen juo teen = drinks the tea (a particular tea, fully).

What case is keittiössä, and why is it -ssä and not -ssa?

Keittiössä is the inessive case, meaning “in(side) the kitchen.” The inessive ending is -ssa/-ssä. Finnish has vowel harmony:

Back vowels (a, o, u) take back endings (-ssa).
Front vowels (ä, ö, y) take front endings (-ssä). Because keittiö contains the front vowel ö, it takes -ssä → keittiössä.

How would I say “into the kitchen” and “out of the kitchen”?

Use the other interior local cases:

Illative (into): keittiöön
Elative (out of): keittiöstä

So: “into the kitchen” = keittiöön, “out of the kitchen” = keittiöstä.

Finnish present tense juo looks like “drinks.” How do I say “is drinking” in Finnish?

Finnish present tense covers both simple and progressive meanings, so Aikuinen juo teetä keittiössä can mean either “drinks” or “is drinking.” If you need to emphasize an ongoing action right now, use the construction with olla + -massa/-mässä:

Aikuinen on juomassa teetä keittiössä = is in the middle of drinking tea in the kitchen.

Is the word order fixed, or can I move parts of the sentence around?

Word order is flexible and used for emphasis/information structure. Neutral is SVO:

Aikuinen juo teetä keittiössä. You can front the place for emphasis:
Keittiössä aikuinen juo teetä. (Emphasizes the location.) You can also front the object to contrast it:
Teetä aikuinen juo keittiössä. (As opposed to coffee, for example.) All are grammatical; the nuance changes with focus.

Does Finnish have articles? How do I know if Aikuinen means “an adult” or “the adult”?

Finnish has no articles. Aikuinen can mean “an adult” or “the adult,” and context decides. Word order, prior mention, and specificity of the object (e.g., teen) help convey definiteness.

Why is the subject Aikuinen (nominative) and not Aikuista (partitive)?

In a normal declarative sentence with a verb like juoda, the subject is nominative: Aikuinen. A partitive subject appears mainly in existential-type sentences or negatives indicating non-existence/indefiniteness, e.g.:

Keittiössä on aikuinen. (There is an adult in the kitchen.)
Keittiössä ei ole aikuista. (There is no adult in the kitchen.)

How does the verb juoda conjugate in the present?

It’s a type 2 verb (stem by dropping -da). Present tense:

minä: juon
sinä: juot
hän: juo
me: juomme
te: juotte
he: juovat

How do I negate the sentence?

Use the negative auxiliary ei + the connegative form of the main verb, and keep the object in the partitive:

Aikuinen ei juo teetä keittiössä. (The adult does not drink/is not drinking tea in the kitchen.)

What about the past tense?

Use the imperfect (simple past):

Unbounded/indefinite: Aikuinen joi teetä keittiössä. (drank some tea / was drinking tea)
Bounded/total object: Aikuinen joi teen keittiössä. (drank the tea, all of it)

How do I make the sentence plural?

Pluralize the subject and use the 3rd person plural verb:

Aikuiset juovat teetä keittiössä. The object stays partitive for an indefinite amount.

Why is teetä spelled with -tä, not -ta?

It’s the partitive singular ending -ta/-tä. With only neutral vowels (e, i) in the stem, Finnish uses the front variant -tä by default. Hence tee → teetä.

How do quantities affect the object case, e.g., “a cup of tea” or “a liter of tea”?

With measure words, the measure is typically the (total) object and the substance remains partitive:

Aikuinen juo kupin teetä keittiössä. (a cup of tea; cup = total object, tea = partitive)
More explicitly measured: Aikuinen juo kupillisen teetä / litran teetä.

Can I swap in other drinks? Do they also take the partitive?

Yes. With an indefinite amount, use the partitive:

kahvia (coffee), maitoa (milk), vettä (water), olutta (beer) Examples: Aikuinen juo kahvia/maitoa/vettä/olutta keittiössä. For a specific, bounded drink, use the total object: juo kahvin/maidon/veden/oluen.

Any pronunciation tips for the words here?

Aikuinen: initial ai is a diphthong like English “eye”; stress the first syllable.
juo: uo is a diphthong; pronounce both vowels smoothly.
tee / teetä: ee is a long vowel (hold it); ä is a front vowel (like the a in “cat,” but fronted).
keittiössä: double consonants tt and ss are long; ö is a front rounded vowel (like German ö). Stress on the first syllable: KEIT-ti-össä.

What’s the difference between keittiössä and keittiöllä?

keittiössä (inessive) = in the kitchen (inside the room).
keittiöllä (adessive) = at/on the kitchen (rare here; adessive is used for surfaces, open areas, or certain institutions). For this sentence about being inside a room, keittiössä is the natural choice.

How would I say “in my kitchen” or “in the adult’s kitchen”?

Finnish can use possessive suffixes or genitives:

“in my kitchen”: keittiössäni; full sentence: Aikuinen juo teetä keittiössäni.
“in the adult’s kitchen”: aikuisen keittiössä; full sentence: Aikuinen juo teetä aikuisen keittiössä. (Here the owner of the kitchen is specified separately.)