Learn Hardcore Finnish: Mitä enemmän sataa, sitä vihreämpi puisto on. - The more it rains, the greener the park is.

The pattern “Mitä X‑mpi, sitä Y‑mpi” (or “Mitä enemmän…, sitä…” with enemmän = more) is the Finnish equivalent of English “the more …, the more …” / “the more …, the …‑er”.

So:
Mitä enemmän sataa, sitä vihreämpi puisto on.
≈ The more it rains, the greener the park is.

General pattern:

Mitä + comparative/adverb,
sitä + comparative/adjective/adverb.

Examples:

Mitä nopeammin ajat, sitä vaarallisempaa se on.
= The faster you drive, the more dangerous it is.
Mitä vanhempi auto on, sitä enemmän se maksaa.
= The older the car is, the more it costs.

Why are mitä and sitä used here? Aren’t they question words / demonstratives?

Yes:

mitä is (among other things) the partitive form of mikä (what),
sitä is the partitive form of se (it / that).

In this particular comparative-correlative structure, mitä … sitä … is a more or less fixed pattern that you just have to learn as a unit:

mitä ≈ “the more / the (to whatever extent)”
sitä ≈ “the more / the (to that same extent)”

They don’t translate word‑for‑word in a simple way; it’s better to think:

Mitä X, sitä Y
= The more X, the more Y (or The X‑er, the Y‑er)

Using something like *sen enemmän, sen vihreämpi in this meaning would be unidiomatic; mitä … sitä … is the standard way to express this kind of proportional relationship.

What grammatical case are mitä and sitä in, and why the partitive?

Both mitä and sitä are in the partitive singular:

mikä (what) → mitä (partitive)
se (it/that) → sitä (partitive)

In Finnish, the partitive is often used for:

Quantities and amounts (paljon vettä = a lot of water)
Partialness / “some (of)”
Indefinite, open‑ended extent

In Mitä enemmän sataa, sitä vihreämpi puisto on, you can very roughly feel it as:

mitä enemmän ≈ “(the) more (of it, in amount)”
sitä vihreämpi ≈ “(to that extent) greener”

So the partitive fits the idea of varying degree/amount that changes as something else changes. In practice, this mitä … sitä … is a fixed idiomatic pattern, and you almost always see it in the partitive.

Why is sataa used without a subject? Why not “se sataa” like “it rains”?

Sataa is a typical impersonal weather verb in Finnish. It’s in the 3rd person singular present form, but Finnish doesn’t need a dummy subject like English it.

Sataa. = It’s raining / It rains.
Satoi eilen. = It rained yesterday.

Using se here as a dummy “it” is normally unnecessary and not standard:

*Se sataa. (as a general weather statement) → sounds off/childish or very colloquial at best.

However, se sataa can appear in speech if se refers to a specific thing already mentioned (e.g. se sade “that rain”, se lumisade “that snowfall”). But for normal weather talk and in this type of general sentence, you just say:

Mitä enemmän sataa, sitä vihreämpi puisto on.

What tense are sataa and on here? Could this also refer to the future?

Both sataa and on are in the present tense:

sataa = it rains / it is raining
on = is

Finnish present tense is often used for:

General truths and regular relationships
(Vesi kiehuu sata asteessa. = Water boils at 100 degrees.)
Future events, when the futurity is clear from context.

So:

Mitä enemmän sataa, sitä vihreämpi puisto on.

can cover:

A general law: “As a rule, the more it rains, the greener the park is.”
A kind of future‑like meaning in the right context:
“The more it (will) rain, the greener the park (will) be.”

Finnish doesn’t have a separate future tense; the present plus context does the job.

Why is there a comma in the middle? Can we reverse the order of the two parts?

The sentence consists of two clauses:

Mitä enemmän sataa,
sitä vihreämpi puisto on.

They are closely connected but still separate clauses, so Finnish normally separates them with a comma.

You can reverse the order:

Sitä vihreämpi puisto on, mitä enemmän sataa.

This is grammatically fine. The most common, neutral order is usually:

Mitä … (first), sitä … (second).

Putting the sitä‑clause first can sound a bit more emphatic or stylistically marked, but it is correct.

How is vihreämpi formed, and is there a difference between vihreämpi and enemmän vihreä?

Vihreämpi is the comparative form of the adjective vihreä (green).

Formation of the basic comparative is:

adjective stem + ‑mpi

So:

vihreä → vihreämpi (greener)
pitkä (long/tall) → pidempi (longer/taller)
kaunis (beautiful) → kauniimpi (more beautiful)

For short, ordinary adjectives like colors, ‑mpi is the normal and natural way to form the comparative.

You can technically say enemmän vihreä, but:

It sounds unusual and often awkward here.
Vihreämpi puisto is what native speakers would use.

enemmän + adjective is more common with:

Longer or more “complex” adjectives:
enemmän kiinnostunut (more interested)
Or when emphasizing quantity rather than “more X‑like”:
e.g. enemmän hyödyllinen in some contexts.

In this sentence, vahreämpi puisto is the idiomatic and expected form.

Does vihreämpi agree with puisto in case and number?

Yes. In Finnish, an attributive adjective usually agrees with its noun in:

Number (singular/plural)
Case (nominative, partitive, genitive, etc.)

Here:

puisto is nominative singular;
vihreämpi is also nominative singular.

If the case or number changed, both would change:

Näen vihreämmän puiston.
(I see a greener park. → singular, genitive/object form)
Näen vihreämpiä puistoja.
(I see greener parks. → plural, partitive)
Vihreämmät puistot ovat kauniita.
(The greener parks are beautiful. → plural, nominative)

So vihreämpi puisto is the basic nominative pair.

Could you omit the final on and just say “Mitä enemmän sataa, sitä vihreämpi puisto”?

No, not in standard Finnish. You need the verb on (“is”) here:

Mitä enemmän sataa, sitä vihreämpi puisto on. ✅

Leaving out on would make the second clause incomplete:

*Mitä enemmän sataa, sitä vihreämpi puisto. ❌ (ungrammatical)

Finnish can sometimes drop on in very short, stylized expressions:

Mitä vanhempi, sen parempi. (The older, the better.)
Puisto vihreä. (in headlines, labels, very telegraphic style)

But in a normal full sentence with a clear subject (puisto) and predicate, the copula verb on is required.

What exactly is enemmän here, and how does it relate to paljon?

Enemmän is the comparative form of paljon (a lot, much).

Roughly:

paljon = much / a lot
enemmän = more (of that; a greater amount)

So in Mitä enemmän sataa, you literally have:

“the more (it) rains / the more (rain there is)”

Some key points:

paljon (base adverb)
enemmän (comparative) → more
eniten (superlative) → most

There is a colloquial/dialectal variant enempi, but:

enemmän is the standard written form, and what you should learn first.

Can the “mitä … sitä …” structure be used with other verbs and adjectives in the same way?

Yes. The pattern is very productive. You can plug in many different verbs and adjectives:

Mitä enemmän luen suomea, sitä paremmin ymmärrän.
= The more I read Finnish, the better I understand.
Mitä vähemmän nukun, sitä väsyneempi olen.
= The less I sleep, the more tired I am.
Mitä vanhempi talo on, sitä kalliimpi se on.
= The older the house is, the more expensive it is.
Mitä nopeammin työskentelet, sitä aikaisemmin pääset kotiin.
= The faster you work, the earlier you get home.

The “slots” are:

mitä + comparative form (verb phrase/adjective/adverb)
sitä + corresponding comparative form

The sentence Mitä enemmän sataa, sitä vihreämpi puisto on is just one specific instance of this very general pattern.