Learn Hardcore Finnish: Lukko estää minua avaamasta ovea. - The lock prevents me from opening the door.

estää is a transitive verb meaning “to prevent” or “to stop.” In Finnish, when you want to say “prevent someone from doing something,” you use estää + person (in partitive) + verb-masta (third infinitive elative).

Why is minua in the partitive case instead of minä?

Because estää requires its object (the person being prevented) in the partitive case. The nominative minä becomes minua here. Using minä instead would be ungrammatical.

Why is the verb in the form avaamasta and not the basic infinitive avata?

avaamasta is the third infinitive (elative) converb in its “from …ing” form (commonly called the -masta form). With estää, you must use verb-masta to express “prevent from doing.” The first infinitive avata can’t carry that meaning.

What does the suffix -masta in avaamasta indicate?

The -masta suffix marks the elative case of a verbal noun, translating roughly as “from …ing.” It shows that the action (opening) is what’s being prevented: “from opening.”

Why is ovi rendered as ovea in this sentence?

Within the clause avaamasta ovea, ovea is in the partitive case because objects of non-finite verb forms (like converbs or verbal nouns) take the partitive. You can view avaamasta ovea as “from opening the door,” where door is partitive.

Can you omit minua and say Lukko estää avaamasta ovea?

No. estää is transitive and needs a direct object (the person prevented). Without minua, there is no “who” in the sentence. If you want to avoid specifying the person, you can rephrase impersonally or passively, for example:

Ovi ei aukea lukon takia. (The door doesn’t open because of the lock.)
Lukko estää oven avaamisen. (The lock prevents the opening of the door.)

Could I rephrase the sentence using a noun instead of the -masta form, for example oven avaamisesta?

Yes. Turn avata into the noun avaaminen and use its elative -sta:
Lukko estää minua oven avaamisesta.
Here oven is genitive (modifying avaaminen) and avaamisesta means “from opening,” so the meaning stays the same.