Learn Hardcore Finnish: Vien ostoskorin kassaan ja maksan pankkikortilla. - I take the shopping basket to the checkout and pay by bank card.

Vien is the 1st person singular present tense form of the verb viedä (to take / to bring).
Verb pattern (present tense): minä vien, sinä viet, hän vie, me viemme, te viette, he vievät.
Finnish often omits the subject pronoun (minä) because the verb ending already shows who is doing it.

Does viedä mean take or bring? How do I choose?

Viedä can correspond to either take or bring depending on viewpoint and context. In a shop situation, English often says take (it) to the checkout, while Finnish naturally uses viedä for moving something to another place. If you wanted to emphasize bringing something to someone (like “bring it to me”), you might also see tuoda, but here viedä is the normal choice.

Why is it ostoskorin and not ostoskori?

Ostoskorin is the genitive form (ending -n). With many common action verbs (including viedä), the object is often in the genitive when the action is seen as completed/whole (a “total object”).

Vien ostoskorin = “I take the (whole) basket.”
If you used a partitive object, it would suggest an incomplete/ongoing action or an indefinite amount, but with ostoskor(i) as a countable item, the genitive is very typical here.

Is ostoskorin genitive or accusative? I’ve heard Finnish has an accusative.

In Finnish, the “accusative” for many nouns looks exactly like the genitive -n in the singular. Many textbooks describe ostoskorin here as a total object in the accusative, but the form you actually see is -n, identical to the genitive. Practically, learners can remember: singular total object often ends in -n.

What case is kassaan, and what does it mean?

Kassaan is the illative case, meaning into or to inside something.

kassa = checkout/cash register (also “cash desk”)
kassaan = “into the checkout area / to the checkout (as a destination)”
Illative often answers “where to?” with a sense of entering or moving into a place.

Why is it kassaan and not kassalle?

Both are possible depending on the nuance and what you imagine as the “place”:

kassalle (allative) = “to the checkout” as a point/surface/destination (very common)
kassaan (illative) = “into the checkout (area/line)” / “to the cashier position” with a slightly more “into” feel
In everyday speech, many people say Vien ostoskorin kassalle, but kassaan is also acceptable.

Why are there no words for I or my in the sentence?

Finnish usually drops subject pronouns because the verb ending shows the person: vien, maksan already mean I take, I pay.
Also, Finnish often avoids possessives when the context is obvious. Ostoskorin here is just “the basket (I have)”; you don’t need minun (my).

What does ja do here, and does it affect word order?

Ja means and, linking two clauses:

Vien ostoskorin kassaan (I take the basket to the checkout)
(ja) maksan pankkikortilla (and I pay with a bank card)
Finnish word order is fairly flexible, but the neutral order is verb + object + place in the first clause and verb + manner in the second.

Why is it maksan and not some future tense like I will pay?

Finnish has no dedicated future tense. The present tense is used for present and near-future actions, and context supplies the timing. In a sequence like this, maksan naturally means “(then) I pay / I’m going to pay.”

What case is pankkikortilla, and why is it used for “with”?

Pankkikortilla is in the adessive case (-lla/-llä), which can express “on/at” and also means/instrument, often translated as with:

pankkikortti = bank card / debit card
pankkikortilla = “with a bank card” / “by bank card”
It’s the normal way to express payment method: Maksan kortilla.

Is pankkikortti specifically a debit card? What if it’s a credit card?

In everyday Finnish, pankkikortti usually refers to a debit card (a “bank card”). For credit card, you’d typically say luottokortti. If you just say kortilla, it can cover either, depending on context.

Why does kassa become kassaan with double s and double a?

Two different things are happening: 1) Double s: the base word is already kassa (with ss).
2) Double a in kassaan: the illative is formed by adding -Vn (a vowel + n) and often results in a long vowel: kassa + an → kassaan.
You’ll see the same pattern in many words: talo → taloon, kauppa → kauppaan.

Could I say Vien ostoskorin kassalle ja maksan kortilla? Would it sound more natural?

Yes—Vien ostoskorin kassalle ja maksan kortilla is very natural and probably the most common everyday version.
Your original sentence is also correct; it just uses kassaan and the more specific pankkikortilla.