Learn Hardcore Finnish: Varmistan, että kirjoitan henkilötunnuksen oikein lomakkeeseen. - I make sure that I write the personal identity code correctly on the form.

Both are seen, but the comma is standard in careful writing when a main clause is followed by an että-clause. The että-clause is a subordinate clause functioning as the object/complement of varmistaa (to make sure / to ensure), and Finnish punctuation typically separates it with a comma:

Varmistan, että kirjoitan... = I make sure that I write...

In very informal texting, the comma may be dropped, but in formal Finnish (like forms, instructions, official contexts) you should keep it.

What exactly does että do here?

että introduces a subordinate clause meaning that (a content clause). The whole että kirjoitan henkilötunnuksen oikein lomakkeeseen answers what you are ensuring.

Compare:

Tiedän, että... = I know that...
Luulen, että... = I think that...
Varmistan, että... = I make sure that...

Why is it kirjoitan (present tense) if this is about something I’m going to do?

Finnish often uses the present tense for near-future or planned actions when the context already implies the future. Here, “I make sure (now) that I write it correctly (when I fill it in).” English often prefers will write, but Finnish doesn’t need a separate future tense.

If you want to emphasize the future more explicitly, you can add a time expression:

Varmistan, että kirjoitan sen oikein huomenna. = I make sure I write it correctly tomorrow.

Why is the verb in the subordinate clause kirjoitan in the 1st person? Could it be passive?

It’s 1st person because the subject is I: I make sure that I write... Finnish keeps the person marking inside the että-clause:

Varmistan, että kirjoitan... = I ensure that I write...

A passive would shift meaning toward “it gets written” / general instruction:

Varmistetaan, että henkilötunnus kirjoitetaan oikein lomakkeeseen. = We/people make sure that the personal identity code is written correctly on the form.
That’s more like an impersonal guideline.

What is henkilötunnuksen grammatically, and why does it end in -n?

henkilötunnuksen is the genitive/accusative-looking -n form used here as the object of kirjoittaa (to write). In Finnish, many total/definite objects appear with -n in singular.

Base form: henkilötunnus = personal identity code
Object form here: henkilötunnuksen = (the) personal identity code (as the thing being written)

This sentence treats the object as a complete whole: you’re writing the entire code.

How do I know whether the object should be henkilötunnuksen or henkilötunnusta?

Very commonly:

-n / nominative (total object) when the action is seen as completed/whole or definite:
kirjoitan henkilötunnuksen = I write the (whole) code (correctly).
-ta/-tä (partitive object) when it’s ongoing, incomplete, or “some of it,” or in certain negative contexts:
kirjoitan henkilötunnusta can suggest “I’m in the process of writing the code” or focuses less on completion.

In real use, when talking about entering a specific ID code into a form, henkilötunnuksen is the natural choice.

What case is lomakkeeseen, and why that ending?

lomakkeeseen is illative case, expressing movement into something:

lomake = form
lomakkeeseen = into the form (i.e., into the fields/spaces on the form)

Finnish uses location cases instead of prepositions like “into/on/in”:

lomakkeessa = in/on the form (inessive: location)
lomakkeeseen = into the form (illative: direction)

Why is it lomakkeeseen (“into the form”) instead of lomakkeelle (“onto the form”)?

Both can be possible depending on how you conceptualize the “surface” vs “inside” idea:

lomakkeeseen = into the form (into the blanks/fields) — very common for filling in.
lomakkeelle = onto the form (onto the sheet/document) — also possible, slightly more “on the page.”

In practice, lomakkeeseen is a very typical choice for entering information in designated fields.

Where does oikein fit grammatically, and what does it modify?

oikein is an adverb meaning correctly. It modifies the verb kirjoitan:

kirjoitan ... oikein = I write ... correctly

Word order is flexible, but this placement is very natural. You could also say:

Varmistan, että kirjoitan oikein henkilötunnuksen lomakkeeseen. This shifts emphasis slightly to “correctly,” but the meaning stays the same.

Could this be said without an että-clause?

Yes. A common alternative is an infinitive construction:

Varmistan kirjoittavani henkilötunnuksen oikein lomakkeeseen. = I make sure (that) I write the personal identity code correctly on the form.

This is more compact and a bit more “written style.” The että-clause version is very clear and common in both speech and writing.

Does varmistaa mean “to confirm” or “to make sure”? How strong is it?

varmistaa can cover both, depending on context:

to make sure / ensure (taking steps so something is correct)
to confirm / verify (checking that something is true/correct)

In your sentence, it’s “make sure/ensure” in a practical sense: you’re checking so you enter the ID code correctly.

Is henkilötunnus the same as “social security number”?

Not exactly. henkilötunnus is the Finnish personal identity code (often abbreviated hetu). English speakers sometimes loosely compare it to a “social security number,” but it’s a different system. In translation, personal identity code is the standard, accurate term.

What is the basic dictionary form of the words in the sentence?

Varmistan → varmistaa (I ensure/make sure)
että → että (that)
kirjoitan → kirjoittaa (I write)
henkilötunnuksen → henkilötunnus (personal identity code)
oikein → oikein (correctly)
lomakkeeseen → lomake (form) + illative -seen (into)

Is the word order fixed, or could it be rearranged?

Finnish word order is relatively flexible, and changes mainly affect emphasis. The given order is neutral and natural. Variations are possible:

Varmistan, että kirjoitan lomakkeeseen henkilötunnuksen oikein. (emphasis slightly later)
Varmistan, että henkilötunnuksen kirjoitan lomakkeeseen oikein. (strong emphasis on the object; can sound marked)

For a learner, keeping the original order is a good default.