Learn Hardcore Finnish: Tilaan joko teen tai kahvin. - I will order either tea or coffee.

joko … tai explicitly sets up an either–or choice (mutually exclusive by default).
Plain tai can be inclusive in general statements, but in a context like ordering a drink it’s naturally understood as one or the other anyway.
All of these are acceptable, with slightly different emphasis:
- Tilaan joko teen tai kahvin. (clear either–or)
- Tilaan teen tai kahvin. (neutral; context makes it either–or)

Why are teen and kahvin in the -n form? Which case is this?

It’s the singular “total object” form, which for common nouns is the genitive (-n). Many grammars also call this the accusative of nouns, since it functions as the completed/whole object.
You use it when the object is a whole, bounded thing (here: one tea/one coffee as a portion).

Could I say Tilaan joko teetä tai kahvia instead? What’s the difference?

Yes. teetä/kahvia (partitive) presents an unbounded/unspecified amount: “some tea/coffee.”
teen/kahvin (genitive) presents a bounded portion: “a tea/a coffee” (implicitly one serving).
In cafés both are common. Partitive sounds like “I’ll have coffee (in general),” genitive like “I’ll have a coffee (one portion).”

Do both alternatives have to be in the same case after joko … tai?

Yes, keep the forms parallel. Each conjunct shows the same case:
- ✓ Tilaan joko teen tai kahvin.
- ✓ Tilaan joko teetä tai kahvia.
- ✗ Tilaan joko tee tai kahvin. (mismatch)

Why is it teen and not teet? Isn’t teen also “I do”?

Here teen = genitive of the noun tee (tea).
teet is the 2nd person singular of the verb tehdä (you do).
There is an accidental homonymy: teen can also be “I do” (from tehdä). In this sentence, the verb is already tilaan (I order), so teen must be the noun “tea” in genitive.

Can I leave out joko? Does it change the meaning?

Yes: Tilaan teen tai kahvin is perfectly normal.
joko just highlights the either–or structure. Without it, context still implies you’ll pick one.

Should it be tai or vai?

In statements: use tai.
In direct questions: use vai.
- Statement: Tilaan joko teen tai kahvin.
- Question: Tilaatko teen vai kahvin?

Is tilaan present or future? Why no future tense?

Finnish has no separate future tense. The present covers future meanings when context implies it.
Tilaan can mean “I order/I’m going to order/I’ll order,” depending on context.

Where can joko appear? Can I put it before the verb?

joko should come right before the first of the two parallel alternatives.
- Objects: Tilaan joko teen tai kahvin.
- Whole clauses: Joko tilaan teen tai lähden pois. (either I order tea or I leave)
Don’t do: ✗ Joko tilaan teen tai kahvin (the two alternatives must be the same kind of unit; here one is a clause and the other just a noun phrase).

Why is there no article like “a”? How do I say “a cup of …”?

Finnish has no articles. The -n object form often implies a single portion.
To be explicit:
- Tilaan yhden kahvin. (I’ll order one coffee.)
- Tilaan kupin teetä. (a cup of tea; measure word + partitive of the drink)
- Tilaan kupin kahvia. (a cup of coffee)

How do I say this with sizes or adjectives?

Adjectives agree in case with the noun:
- Genitive (bounded portion): Tilaan joko pienen teen tai ison kahvin.
- Partitive (some amount): Tilaan joko pientä teetä tai isoa kahvia.

How would the sentence look in the negative?

Negation requires the partitive object:
- En tilaa teetä enkä kahvia. (I won’t order tea or coffee.)
Note enkä = “nor” after a negated clause.

Does tilata only mean “to order in a restaurant”?

No. tilata also means:
- to order goods/services: tilata taksi, tilata pitsa
- to subscribe: tilata lehti (subscribe to a magazine/newspaper)

Any quick pronunciation tips for tee/teen and kahvi/kahvin?

tee has a long vowel: [teː]. teen adds an [n] at the end: [teːn].
kahvi pronounces the h clearly: [kɑhʋi]. kahvin ends with
The noun teen and the verb form teen (“I do”) sound the same; context disambiguates.