Learn Hardcore Finnish: Tämä viesti on kirjoitettu selvästi.

Tämä = this (demonstrative pronoun used here like a determiner: this message).
Viesti = message in the nominative singular, which is the basic dictionary form.

In Finnish, the subject is typically in the nominative case and often has no visible ending (unlike many objects or other roles, which take endings like -n, -lle, -ssa, etc.). That’s why both tämä and viesti appear in their basic forms here.

Why is it Tämä viesti, not Tämän viesti?

Tämä viesti is like saying this message in English: tämä is in the nominative, matching the subject viesti in the nominative.

Tämän is the genitive form (like of this or this one’s). You would use tämän before a noun when that noun is in the genitive construction, for example:

Tämän viestin otsikko = The title of this message (literally: this message’s title).

In the sentence Tämä viesti on kirjoitettu selvästi, we just have a simple subject, so nominative tämä is correct.

What exactly does on kirjoitettu mean in terms of tense and voice?

On kirjoitettu is:

Tense: perfect
Voice: passive (sometimes called the “impersonal” in Finnish)

Literally, it is:

on = is / has (3rd person singular of olla, to be)
kirjoitettu = written (past passive participle of kirjoittaa, to write)

Together they correspond to has been written or is written in English, depending on context:

Tämä viesti on kirjoitettu selvästi.
→ This message has been written clearly / This message is written clearly.

It refers to a completed writing action whose result still matters now. The doer is not mentioned (and is in fact grammatically irrelevant in the Finnish passive).

How is kirjoitettu formed from the verb kirjoittaa?

The base verb is kirjoittaa (to write).

For the past passive participle, Finnish generally:

Takes the passive stem: kirjoiteta- (from present passive kirjoitetaan = is written / is being written).
Replaces -ta with -ttu (a common participle ending after a vowel).

So:
kirjoittaa → kirjoiteta- → kirjoitettu

This form kirjoitettu is used in:

Perfect passive: on kirjoitettu = has been written
As an adjective-like form: kirjoitettu viesti = a written message

Could I leave out on and say Tämä viesti kirjoitettu selvästi?

No, that would be incorrect in normal standard Finnish.

You need the auxiliary verb on to form the perfect passive:

Tämä viesti on kirjoitettu selvästi. ✅
Tämä viesti kirjoitettu selvästi. ❌ (sounds like broken or telegraphic Finnish)

Without on, the sentence is missing its finite verb, so it feels unfinished.

Why is the passive used here instead of an active form like joku on kirjoittanut?

Both are possible, but they have different focus:

Tämä viesti on kirjoitettu selvästi.
→ Passive: focus on the message and the result, not on who wrote it.
Joku on kirjoittanut tämän viestin selvästi.
→ Active: someone (unspecified) has written this message clearly; the doer is mentioned (joku).
Finnish passive is often used:
When the doer is unknown or unimportant.
When you want an impersonal tone (instructions, formal texts, announcements).

Here, we care about the clarity of the message, not about the writer, so the passive is natural.

Could the sentence also mean “This message is obviously written” because of selvästi?

Selvästi can indeed mean:

Clearly (in terms of clarity / being easy to understand).
Obviously / clearly (in the sense of evidently).

In Tämä viesti on kirjoitettu selvästi, the most natural interpretation is:

This message has been written clearly (the text itself is clear).

However, in other contexts, selvästi can mean obviously:

Hän on selvästi väsynyt.
→ He/She is clearly / obviously tired.

In your sentence, the adverb describes the manner of writing, so clearly (in the sense of in a clear way) is the intended meaning.

How is selvästi formed, and what is the difference between selvä and selvästi?

Base adjective: selvä = clear.

Adverb: selvästi = clearly.

The pattern is:

selvä → selvästi (add -sti to the -ä form, with vowel harmony).

Usage:

Adjective (selvä): modifies a noun.
- selvä viesti = a clear message
Adverb (selvästi): modifies a verb or a whole sentence.
- Viesti on kirjoitettu selvästi. = The message has been written clearly.

So selvästi tells us how the writing was done.

Can selvästi appear in a different position, like Tämä viesti on selvästi kirjoitettu?

Yes, that is also correct, but the nuance shifts slightly.

Tämä viesti on kirjoitettu selvästi.
Focus: written in a clear way (manner of writing).
Tämä viesti on selvästi kirjoitettu.
More like: It is clear/obvious that this message has been written (or it’s clearly written, with a bit more emphasis on your assessment).

In real life, both can sometimes overlap, but:

[kirjoitettu selvästi] = adverb strongly tied to the verb’s manner.
[selvästi kirjoitettu] = adverb more tied to your judgment (clearly / obviously written).

What is the difference between Tämä viesti on kirjoitettu selvästi and Tämä viesti kirjoitettiin selvästi?

Both use the passive, but the tense differs:

Tämä viesti on kirjoitettu selvästi.
- Perfect passive.
- Emphasizes the result that is relevant now.
- This message has been written clearly / is written clearly.
Tämä viesti kirjoitettiin selvästi.
- Simple past passive.
- Refers to a past event at some specific time.
- This message was written clearly (then).

In Finnish, the perfect (on kirjoitettu) is used when the result still matters or is visible now; the past (kirjoitettiin) just situates the action in the past.

Is the word order Tämä viesti on kirjoitettu selvästi fixed, or can I change it?

Finnish word order is more flexible than English, though there are default patterns. The normal neutral order here is:

Tämä viesti on kirjoitettu selvästi.

Other possible orders (with different emphasis) include:

Selvästi tämä viesti on kirjoitettu.
→ Emphasis on selvästi (you’re stressing clearly).
Tämä viesti on selvästi kirjoitettu.
→ Emphasis on your assessment that it is clearly written.

However, you cannot break the verb phrase on kirjoitettu incorrectly (e.g. on selvästi kirjoitettu is fine, but something like kirjoitettu on selvästi changes focus and sounds marked or poetic). For learners, it’s safest to stick to:

Tämä viesti on kirjoitettu selvästi.

How do you pronounce kirjoitettu, especially the double tt?

Key points:

kir-joit-et-tu (four syllables): KIR-joit-et-tu.
rj: r is trilled or tapped; j is like English y in yes.
oi: like oy in boy, but shorter and more pure.
e: like e in get.
u: like oo in book (short).
Double tt (-tt-) is pronounced as a long / geminated t:
- Hold the t a bit longer than a single t.
- For learners, think of a tiny pause between the vowels: kir-joit-et-tu vs. kir-joite-tu.

Length matters in Finnish: t vs. tt can distinguish different words and forms.

Could I say Tämä viesti on kirjoitettu selväksi instead of selvästi?

You can, but the meaning changes.

selvästi = clearly, in a clear manner.
- Tämä viesti on kirjoitettu selvästi.
  → The way the message is written is clear; it’s easy to understand.
selväksi = into a clear state, translative case.
- Tämä viesti on kirjoitettu selväksi.
  → The message has been written so that it becomes clear (changed from unclear to clear).

In many everyday contexts the difference is subtle, but grammatically:

selvästi describes how it was written (manner).
selväksi describes what state it was brought into (resulting state).