Learn Hardcore Finnish: Maanantai on usein kiireinen päivä.

Weekday names (maanantai, tiistai, keskiviikko, etc.) are normally not capitalized in the middle of a sentence.
In this sentence, Maanantai is capitalized simply because it is the first word of the sentence, not because it’s a weekday name.

So:

Maanantai on usein kiireinen päivä. – at the start: capital M
Pidän maanantaista. – in the middle: lowercase m

Why is there no word like “a” or “the” before kiireinen päivä?

Finnish has no articles (no equivalents of English a/an or the).

The bare noun päivä can mean:

a day
the day
sometimes just day in a general sense

Context decides. Here, kiireinen päivä is naturally understood as “a busy day.”

What case are Maanantai and päivä in, and why?

Both Maanantai and päivä are in the nominative (the “basic” dictionary form).

In Finnish, with the verb olla (“to be”):

The subject is in the nominative: Maanantai
The predicative (what the subject is) is also in the nominative: kiireinen päivä

So the pattern is:

[Subject in nominative] + on + [predicative in nominative]
Maanantai on kiireinen päivä.
Monday is a busy day.

Why is the adjective kiireinen in that form? Why not something like kiireista?

Kiireinen is an adjective meaning “busy.” Adjectives usually:

Agree with the noun in case and number.
Here, päivä is singular nominative, so the adjective should also be singular nominative → kiireinen.

You see the same pattern in other sentences:

Tämä on hyvä kirja. – “This is a good book.”
- hyvä (adj, nominative) + kirja (noun, nominative)

Forms like kiireistä / kiireisen / kiireisiä are other cases and numbers; they’re not used here because the structure is a simple X is Y with both parts in the basic form.

Why does the adjective come before the noun, kiireinen päivä, and not after it?

In Finnish, the normal order is:

adjective + noun

So:

kiireinen päivä – busy day
iso talo – big house
kylmä vesi – cold water

Putting the adjective after the noun is not standard in this kind of simple noun phrase. So you wouldn’t say päivä kiireinen to mean “busy day.”

Why is on used here? Isn’t the infinitive of “to be” olla?

Yes, olla is the infinitive “to be.” It conjugates:

minä olen – I am
sinä olet – you (sg) are
hän on – he/she/it is
me olemme – we are
te olette – you (pl) are
he ovat – they are

In Maanantai on usein kiireinen päivä. the subject is Maanantai (Monday = “it”), so we use the 3rd person singular form:

on = “is”

Can usein be placed in another position, like at the beginning of the sentence?

Yes. Usein (“often”) is relatively flexible in word order. The most neutral here is:

Maanantai on usein kiireinen päivä.

But you can also say:

Usein maanantai on kiireinen päivä. – Often, Monday is a busy day.
Maanantai on kiireinen päivä usein. – Possible, but more marked/emphatic; sounds a bit unusual in everyday speech.

In general, putting usein right after on is very natural and common.

Could you leave out on and just say Maanantai usein kiireinen päivä?

No. Finnish requires the verb in this kind of sentence.

Maanantai on usein kiireinen päivä. – correct
Maanantai usein kiireinen päivä. – incorrect (missing the verb on)

Unlike some languages that can drop “is” in certain structures, Finnish keeps on (or other forms of olla) in basic “X is Y” sentences.

How would I say “Mondays are often busy days” in Finnish, and how is it different from this sentence?

One natural plural version is:

Maanantait ovat usein kiireisiä päiviä.
- Maanantait – Mondays (plural subject, nominative plural)
- ovat – are (3rd person plural of olla)
- usein – often
- kiireisiä – busy (plural, partitive)
- päiviä – days (plural, partitive)

But Finnish more commonly uses an adverbial form for a generic “on Mondays” idea:

Maanantaisin on usein kiireistä. – “On Mondays it is often busy.”

Compared with the original:

Maanantai on usein kiireinen päivä. – speaking about Monday as a kind or typical day.
Maanantaisin on usein kiireistä. – speaking about how things typically are on Mondays in general.