Suhde on tärkeä molemmille.

A word-by-word breakdown is:

• suhde = relationship
• on = is
• tärkeä = important
• molemmille = to both / for both

So the sentence structure is very close to:

• The relationship is important to both.

Finnish does not normally use articles like a or the.

So suhde can mean:

• a relationship
• the relationship

The exact meaning depends on context. In this sentence, English often uses the relationship, but Finnish simply says suhde.

Because the sentence means important to both, not both are important.

With tärkeä (important), Finnish usually marks the person affected with the allative case, which often corresponds to English to or for:

• tärkeä minulle = important to me
• tärkeä sinulle = important to you
• tärkeä heille = important to them
• tärkeä molemmille = important to both

So molemmille is the correct form here because it means to both.

It is the allative plural form.

The allative often answers the question to whom? or for whom?

Here:

• molemmille = to both

This is a very common pattern in Finnish with adjectives like:

• tärkeä jollekin = important to someone
• hyödyllinen jollekin = useful to someone
• vaikea jollekin = difficult for someone

The basic dictionary form is usually given as molemmat, meaning both.

But in oblique cases, the word often uses the stem molempi-:

• nominative: molemmat = both
• genitive: molempien = of both
• allative: molemmille = to both

So even though the form looks different, it belongs to the same word family.

Because tärkeä describes suhde, not molemmille.

The subject is:

• suhde = relationship

That noun is singular, so the adjective is also singular:

• suhde on tärkeä = the relationship is important

The word molemmille only tells us to whom it is important.

Because the subject is singular:

• suhde = relationship

So Finnish uses the singular verb:

• suhde on = the relationship is

If the subject were plural, the verb would change:

• suhteet ovat tärkeitä molemmille = the relationships are important to both

Yes. Finnish word order is fairly flexible, and changing it often changes the emphasis rather than the basic meaning.

For example:

• Suhde on tärkeä molemmille. = neutral
• Molemmille suhde on tärkeä. = emphasizes to both
• Suhde on molemmille tärkeä. = also natural, with a slightly different rhythm/focus

The original sentence is a very normal, neutral way to say it.

No. Suhde can mean different kinds of relationship, depending on context.

It can refer to:

• a romantic relationship
• a connection between people
• a relation between things
• even an affair in some contexts

So the exact meaning depends on the situation. If the learner was shown the translation already, context tells you what kind of relationship is meant.

Because molemmat is the nominative form, and that would not fit the grammar here.

Compare:

• Molemmat ovat täällä. = Both are here.
  
  • Here molemmat is the subject.

But in your sentence, both is not the subject. It means to both, so Finnish needs:

• molemmille

So the ending is necessary because Finnish shows grammatical roles with cases.

Yes. In natural English, either can work depending on the sentence.

• important to both is the most direct translation
• important for both may also sound natural in some contexts

But grammatically, Finnish uses molemmille, which corresponds most directly to to both.

Sometimes yes, but the nuance is a little different.

• molemmille = to both
• kummallekin = to each of the two / to both individually

In many everyday contexts, they can be very close in meaning. But molemmille is the most straightforward choice in this sentence.

Roughly like TAIR-keh-ah, but with Finnish sounds:

• ä is not the same as English a
• the r is rolled or tapped
• stress is on the first syllable: TÄR-ke-ä

Also, ä and a are different vowels in Finnish, so it is important to keep the dots.

Yes. It is a completely natural and complete sentence.

It has:

• a subject: suhde
• a verb: on
• an adjective complement: tärkeä
• a phrase showing to whom: molemmille

So it is a normal, idiomatic Finnish sentence.