Ihme tapahtui eilen.

Tapahtui is the third-person singular past tense form of tapahtua. So grammatically, it means happened.

A useful comparison is:

• infinitive: tapahtua
• present: tapahtuu
• past: tapahtui

No. Finnish word order is fairly flexible, although some orders sound more neutral than others.

Ihme tapahtui eilen is a normal, straightforward sentence.

You could also say:

• Eilen tapahtui ihme.

That version puts more focus on yesterday or sets the time first. Both are natural.

Because tapahtua is an intransitive verb. That means it does not take a direct object.

The thing that happens is expressed as the subject, not as an object. So ihme is the subject, not something being acted on.

The verb is singular because the subject ihme is singular.

If the subject were plural, the verb would also be plural. For example:

• Ihmeet tapahtuivat eilen.

So Finnish verbs agree with the subject in number.

No. Finnish does not use a dummy subject like English sometimes does with it.

In this sentence, ihme already functions as the subject, so nothing extra is needed.

Yes. Time adverbs like eilen are often quite movable in Finnish. The most natural position depends on what you want to emphasize.

For example:

• Ihme tapahtui eilen. — neutral
• Eilen tapahtui ihme. — emphasizes the time more

A different order may still be grammatical, but some versions can sound more marked or literary.

It is the simple past form in Finnish, often called the imperfect in Finnish grammar. English learners sometimes compare it with happened, not has happened.

So tapahtui is a finished past event.