Learn Hardcore Finnish: Opettaja muistuttaa, että aivot oppivat parhaiten, kun en valvo yöllä vaan nukahdan suurin piirtein samaan aikaan joka ilta. - The teacher reminds us that the brain learns best when I do not stay up at night but fall asleep at roughly the same time every evening.

In Finnish, aivot (brain) is grammatically plural-only, like scissors or pants in English. You don’t normally say aivo in the singular about a person’s brain in everyday language.

Because aivot is plural, the verb must also be plural:

aivot oppivat = the brain learns
literally: brains learn

This is just a quirk of how Finnish treats this noun. It does not imply several brains; it’s just the normal way to say the brain in standard Finnish.

Why is there no minä (I) in kun en valvo yöllä vaan nukahdan…? How do we know it’s “I don’t stay up at night but (I) fall asleep…”?

Finnish usually drops personal pronouns when the verb ending already shows the person.

en valvo → the -n in en and the bare stem valvo together mark 1st person singular (I don’t stay up).
nukahdan → the ending -n marks I fall asleep.

So minä is understood from the verb form and only used when you want to emphasize I (e.g. contrast with someone else).

You could say:

…kun minä en valvo yöllä vaan minä nukahdan…

but it would sound unnecessarily heavy or emphatic in this neutral sentence.

What is the difference between nukahdan and nukun? Why not use nukun here?

Both are from the verb nukkua (to sleep), but:

nukun = I sleep (describes the state of sleeping)
nukahdan = I fall asleep (describes the moment of beginning to sleep)

Nukahdan is an inchoative form (change of state: becoming asleep).

In this sentence, the important thing is when I fall asleep, not just that I sleep. The idea is: the brain learns best when I do not stay awake at night but instead fall asleep at roughly the same time every evening.

If you said kun en valvo yöllä vaan nukun, it would be grammatical but less precise; it would emphasize being in the state of sleeping at night rather than having a regular bedtime.

Why do we use vaan and not mutta in en valvo yöllä vaan nukahdan…?

Both mutta and vaan are often translated as but, but they are used differently:

mutta = but in a general contrast
vaan = but rather / but instead, and it is normally used after a negative clause to correct or replace it

The pattern here is:

en valvo yöllä = I do not stay up at night
vaan nukahdan… = but instead I fall asleep …

So vaan is the natural choice because we have a negation followed by an alternative. With mutta, it would sound off or slightly unidiomatic here.

What does parhaiten mean grammatically? How is it related to hyvä and paras?

The adjective hyvä = good has these key forms:

hyvä = good (positive)
parempi = better (comparative)
paras = best (superlative adjective)

For adverbs, Finnish does not usually use -sti for the superlative. Instead, hyvin (well) becomes:

hyvin = well
paremmin = better (in a better way)
parhaiten = best (in the best way)

So:

aivot oppivat parhaiten = the brain learns best
Literally: brains learn in the best way.

Parhaiten is therefore the superlative adverb corresponding to hyvä/hyvin.

What exactly does muistuttaa, että… mean, and how is it different from muistaa?

Two different verbs:

muistaa = to remember
- Muistan sinut. = I remember you.
muistuttaa = mainly to remind or to point out / to mention as a reminder.
With että, it introduces the content you are reminding about:
- Opettaja muistuttaa, että aivot oppivat parhaiten…
  = The teacher reminds (us) that the brain learns best…

Muistuttaa can also take objects:

Opettaja muistuttaa oppilaita läksyistä.
= The teacher reminds the students about the homework.

Here, muistuttaa, että… is like English remind (us) that… or point out that…. It is not muistaa (to remember).

What is the role of kun in kun en valvo yöllä…? Is it “when” or “because”?

Kun is flexible and can mean:

when (time)
because (informal, causal)

In this sentence:

…että aivot oppivat parhaiten, kun en valvo yöllä vaan nukahdan…

You can understand kun mainly as when:

the brain learns best *when I don’t stay up at night but fall asleep…*

There is also an implied causal idea (this is the reason they learn best), but the most direct English translation is temporal when. Finnish often leaves the causal nuance to context.

Why is yöllä used, and what does this case ending indicate?

Yöllä is the adessive form of yö (night). The adessive ending -lla/-llä often corresponds to:

at / during in time expressions.

So:

yö = night
yöllä = at night / during the night

In en valvo yöllä, it naturally means I don’t stay up at night. This is the usual, idiomatic way to express that idea. Other forms like yönä are possible in different contexts but sound odd or unnatural here.

What does suurin piirtein mean literally, and how is it used? Could we just say noin instead?

Suurin piirtein is an idiomatic phrase meaning approximately / roughly / more or less.

Literally, it comes from something like by the large outline, but in modern language it just equals about, roughly.

In this sentence:

nukahdan suurin piirtein samaan aikaan
= I fall asleep at roughly the same time

You can replace it with noin without changing the meaning much:

nukahdan noin samaan aikaan
This is also very natural.

Nuance: suurin piirtein can feel a bit more informal or conversational and may sound slightly more “roughly, give or take” than noin, but the difference is small.

Why is it samaan aikaan and not something like samalla ajalla? What case is samaan?

Sama (same) in samaan aikaan is in the illative case (direction: into / to).

sama = same
samaan aikaan = at the same time (literally “to the same time”)

In time expressions, Finnish very often uses the illative (-an / -en / -in, etc.) for point in time:

kello kuuteen = until six o’clock
ensi viikkoon = until next week
samaan aikaan = at the same time

Samalla ajalla would sound unusual and not idiomatic for a recurring time point like a bedtime. For at the same time, the fixed expression is samaan aikaan.

Why is it joka ilta and not plural like jokaisena iltana or jokailtana?

All of these exist, but they have slightly different style/feel:

joka ilta
- very common, neutral: every evening / every night
jokaisena iltana
- more formal or emphatic: literally on each evening
jokailta / joka ilta as a compound is less common in standard written language; joka ilta as two words is the usual way.

In speech and neutral writing, joka ilta is the most natural and frequent way to say every evening. That’s why it appears here.

Why are there commas before että and kun in Finnish, even though English often skips them?

Finnish punctuation rules require commas between main clauses and subordinate clauses, more consistently than English.

Opettaja muistuttaa, että aivot oppivat parhaiten, kun en valvo yöllä…

Here:

Opettaja muistuttaa = main clause
että aivot oppivat parhaiten = subordinate että-clause
kun en valvo yöllä… = subordinate kun-clause inside that

Commas are put before both että and kun to mark the clause boundaries.

In English, you might write:
The teacher reminds (us) that the brain learns best when I don’t stay up at night…
and use only one comma or even none. Finnish is more rigid about keeping those clause-separating commas.

Could we drop että and say Opettaja muistuttaa aivot oppivat parhaiten… like in casual English: The teacher reminds the brain learns best…?

No, että cannot be dropped here. In Finnish, että is needed to introduce the content clause functioning as the object of muistuttaa:

Opettaja muistuttaa, että aivot oppivat parhaiten…

Without että, the sentence becomes ungrammatical or changes meaning:

Opettaja muistuttaa aivoja = The teacher reminds the brain(s) (direct object), which is not what we want.

So unlike casual English, Finnish needs että to link the verb muistuttaa to the statement aivot oppivat parhaiten….