Postilaatikko on täynnä mainoksia.

The mailbox is full of advertisements.

Breakdown of Postilaatikko on täynnä mainoksia.

• olla: to be
• täynnä: full
• postilaatikko: the mailbox
• mainos: the advertisement

Questions & Answers about Postilaatikko on täynnä mainoksia.

What type of word is postilaatikko and how is it formed?

Postilaatikko is a compound noun made of posti (‘mail’) + laatikko (‘box’). In Finnish, such compounds are written as one word. So postilaatikko literally means ‘mail-box’.

Why is on used here and what is its role?

On is the third person singular present tense of the verb olla (‘to be’). It links the subject postilaatikko and the predicate täynnä mainoksia, giving “The mailbox is full of ads.”

Why is täynnä used instead of täysi?

Täynnä is a special adjective‐like form that takes a complement in the partitive case (here mainoksia). It expresses the idea “full of something.”
Täysi is a regular adjective (“full”) and would normally take its noun in nominative or genitive (e.g. täysi laatikko = “a full box”), but doesn’t combine with a partitive object to mean “full of X.”

Why is mainoksia in the partitive plural rather than nominative mainokset?

Because täynnä requires its object in the partitive case to indicate “filled with something.” The partitive plural of mainos (‘advertisement’) is mainoksia. It also conveys the sense of “lots of ads” without specifying an exact number.

Where is “the” in this sentence? I don’t see an article.

Finnish has no articles (a/the). Definiteness is understood from context. Postilaatikko on täynnä mainoksia can mean “The mailbox is full of ads” or “A mailbox is full of ads,” depending on what you already know.

How do I say “The mailboxes are full of ads” (plural)?

Make both subject and verb plural:
Postilaatikot ovat täynnä mainoksia.
Here postilaatikot is the nominative plural of postilaatikko, and ovat is the third person plural of olla.

Can I swap the word order for emphasis?

Finnish has fairly flexible word order, but the neutral order is Subject–Verb–Complement (S-V-C). So Postilaatikko on täynnä mainoksia is standard.
You could say Täynnä mainoksia on postilaatikko to stress täynnä mainoksia, but that sounds poetic or marked.

How do I pronounce the long vowels in laatikko and täynnä?

In Finnish, double vowels are long.
– laatikko: [laːtikːo] (long aa)
– täynnä: [tæʏ̯nːæ] (long ä)
Vowel length can change meaning, so it’s important to hold the sound slightly longer than a single vowel.