Learn Hardcore Finnish: Voisitko sinä ilmoittautua kurssille tänään?

It’s the yes/no question particle. In Finnish, the enclitic -ko/-kö attaches to the first element of the clause to form a question. Here it attaches to the verb: voisitko = “could you?”. Moving it to a different word changes the focus:

Voisitko sinä…? neutral yes/no request
Sinäkö voisit…? “Is it you who could…?” (contrastive focus on “you”)

Is the pronoun sinä necessary here?

No. Finnish usually drops subject pronouns because the verb form shows the person. Voisitko ilmoittautua…? is perfectly natural. Adding sinä gives emphasis, roughly “Could you (as opposed to someone else) sign up…?” It doesn’t make the sentence more polite, just more contrastive.

How polite is voisitko compared with voitko?

Voitko…? “Can you…?” Neutral, more direct.
Voisitko…? Conditional “Could you…?” Softer and commonly used for polite requests.
You can soften further: Voisitko …, kiitos? or Voisitko ystävällisesti…?
To be extra formal or when addressing several people: Voisitteko…? (2nd person plural).

What form is voisit and how is it built?

It’s the 2nd person singular conditional of voida (“can, be able to”). The conditional uses the marker -isi-:

voit (you can) → voisit (you could) Adding -ko makes the yes/no question: voisitko (“could you?”).

Why is ilmoittautua in the infinitive?

With voida (“can/could”), Finnish uses the 1st infinitive for the main action: voisitko + [verb in infinitive]. So: voisitko ilmoittautua = “could you register.” You would not conjugate the second verb here.

What’s the difference between ilmoittautua, ilmoittaa (itsensä), and rekisteröityä?

ilmoittautua: intransitive “to sign up/enrol (oneself)” for events, courses, appointments. Most natural here.
ilmoittaa (itsensä): transitive “to notify/register (oneself)”—grammatical but less common in this context; used more for “register someone/something.”
rekisteröityä: “to register (an account), to get registered” (e.g., websites, trademarks, vehicles), not typically for a course.

Why is it kurssille and not kurssiin?

Kurssille is the allative case (-lle, “to/onto”), and with ilmoittautua the target noun often appears either in the allative or illative (-Vn “into”), depending on the noun and convention. For a course, idiomatic Finnish is:

ilmoittautua kurssille (to sign up for a course) Compare: ilmoittautua tenttiin (to an exam, illative) or ilmoittautua kilpailuun (to a competition, illative). Think of it as collocation: with kurssi, use -lle.

Can I move words around? For example, where can tänään go?

Yes. Word order is flexible and affects emphasis:

Neutral: Voisitko (sinä) ilmoittautua kurssille tänään?
Emphasize “today”: Voisitko (sinä) tänään ilmoittautua kurssille? or Tänäänkö voisit…? (question focus on “today”)
Strong focus fronting (marked): Kurssille voisitko (sinä) ilmoittautua tänään?

How do I address multiple people or be formally polite?

Use 2nd person plural:

Voisitteko ilmoittautua kurssille tänään? If you’re formally addressing one person in writing, you can use Te (capital T) with the same verb form: Voisitteko Te…

How would this sound in everyday colloquial speech?

Common spoken options include:

Voisitko sä ilmoittautuu kurssille tänään?
Shorter/softer: Voisiks sä ilmoittautuu…? Notes: sä = spoken “sinä”; infinitive ilmoittautua often sounds like ilmoittautuu in colloquial speech. In careful standard Finnish, keep ilmoittautua.

How can I make the request even more polite?

Add a softener or “please”:

Voisitko ilmoittautua kurssille tänään, kiitos?
Voisitko ystävällisesti ilmoittautua kurssille tänään?
Very courteous: Olisitko ystävällinen ja ilmoittautuisit kurssille tänään? (both verbs in conditional)

How do I say “Is it you who could register today?” for contrast?

Put the question particle on the pronoun:

Sinäkö voisit ilmoittautua kurssille tänään? This questions or highlights that it’s specifically “you.”

How would I say “Couldn’t you register today?” What’s the tone?

Etkö voisi ilmoittautua kurssille tänään? This can sound like urging or mild reproach, depending on context and tone. Softer: Et kai voisi…? or add a mitigating word like ehkä elsewhere in the sentence.

What are natural ways to answer this yes/no request?

Yes: Joo, voin. / Voisin, kyllä. (+ detail: Teeän sen tänään.)
No (lack of time): Valitettavasti en ehdi tänään.
No (lack of ability/permission): En voi tänään. Both present (voin) and conditional (voisin) are used in replies; present is very common.

Could I ask about general possibility instead of asking “you”?

Yes, use an impersonal subject:

Voiko/Voisiko kurssille ilmoittautua tänään? = “Is it (generally) possible to register for the course today?”

Any pronunciation tips, especially for ilmoittautua?

Stress always on the first syllable: IL-moittau-tua.
Double consonant tt is long; don’t shorten it.
au is a diphthong; tua is two syllables (tu-a), so you’ll hear a slight break between u and a.
Keep vowels pure; Finnish vowels don’t reduce like in English.

Can I use other verbs like “have time to” or “be able to” for nuance?

Yes:

Ehtisitkö ilmoittautua…? “Would you have time to register…?”
Pystyisitkö ilmoittautumaan…? “Would you be able to register…?” (with the -maan form) These change the nuance from general permission/possibility (voisitko) to time/ability.

What case would plural “courses” take?

Plural allative: kursseille.

Singular: kurssille
Plural: kursseille Example: Voisitko ilmoittautua kursseille tänään? = “Could you register for the courses today?”