Learn Hardcore Finnish: Pidä pankkikortti mukana, ettet joudu maksamaan käteisellä. - Keep your bank card with you so that you don’t have to pay in cash.

Pidä is the 2nd person singular imperative of pitää (to keep/hold). It’s the form you use for direct instructions to one person: Pidä X mukana = Keep X with you.

Why is the object pankkikortti in the basic form (not pankkikorttia or pankkikortin)?

In Finnish, an imperative often takes a total object, and in the singular imperative that total object is typically nominative-looking (same as the dictionary form):

Pidä pankkikortti mukana. (total object → “keep the card with you” as a complete, bounded idea)

If you used the partitive (pankkikorttia), it would suggest a more ongoing/indefinite or “some of” feeling, which doesn’t fit as well here.

What exactly does pankkikortti mean, and why is it one word?

pankkikortti is a compound: pankki (bank) + kortti (card) → bank card / debit card. Finnish forms compounds very freely, so what English expresses with two words is often one word in Finnish.

What does mukana mean grammatically—what case is it?

mukana functions as an adverb meaning with (you), along, accompanying. Historically it’s related to a case form, but in modern Finnish you can treat mukana as a fixed adverb used with verbs like pitää/ottaa:

Pidä X mukana = keep X with you
Ota X mukaan = take X with you

A more explicitly “with you” alternative is mukanasi (with the possessive suffix), but mukana is extremely common and natural.

Why is there a comma before ettet?

Because the sentence has a main clause + a subordinate clause:

Main clause: Pidä pankkikortti mukana
Subordinate clause (purpose/avoidance): ettet joudu maksamaan käteisellä

Finnish normally separates these with a comma.

What does ettet mean, and why isn’t there a separate word for “not” (like et)?

ettet is essentially “so that you don’t …” / “lest you …”. It’s the negative purpose conjunction ettei with a personal ending attached:

etten = so that I don’t
ettet = so that you don’t
ettei = so that he/she doesn’t
ettemme, ettette, etteivät etc.

Because the negation is built into ettet, you do not add a separate et.

Why is it joudu and not joudut?

After negation in Finnish, the main verb is typically in the connegative form (a special form without personal ending). In this structure, ettet already carries the person (“you”) and the negation, so the verb stays connegative:

ettet joudu (not ettet joudut)

What does the verb joutua imply here?

joutua often means to end up having to, or to be forced/obliged by circumstances. It suggests an unwanted situation you might fall into:

joutua tekemään jotakin = to end up having to do something

So the sentence is advising you to avoid getting stuck in the situation where you must pay cash.

Why is it maksamaan and not maksaa?

After joutua, Finnish commonly uses the MA-infinitive in the illative: tekemään (“into doing” → “to do” in this pattern):

joutua maksamaan = to end up having to pay
joutua odottamaan = to end up having to wait

So maksamaan is the standard construction with joutua.

Why is käteisellä in that form—what case is it, and what does it express?

käteisellä is adessive (ending -lla/-llä). With payment methods, Finnish often uses adessive to mean by means of / using:

maksaa käteisellä = pay in cash
maksaa kortilla = pay by card

So it’s “with cash” in the sense of “using cash as the method”.

Could I say the same idea with jotta instead of ettet?

Yes. A very common alternative is:

Pidä pankkikortti mukana, jotta et joudu maksamaan käteisellä.

Here jotta introduces the purpose clause, and then you use normal negation inside it (et) rather than the built-in negative conjunction ettet. Both are natural; ettet is a bit more compact.

How would this change if I wanted to address someone politely or in plural?

If you address multiple people (or use the polite plural te), you’d change the imperative and the ette- form:

Pitäkää pankkikortti mukana, ettette joudu maksamaan käteisellä.

(pitäkää = imperative plural; ettette = “so that you (pl.) don’t”).