Vi har ombestemt oss.

The basic form is å ombestemme seg.

A few useful parts:

• å bestemme = to decide
• om- = a prefix that often adds the idea of again, differently, or changing
• seg = a reflexive pronoun, part of the verb here

So å ombestemme seg means to change one’s mind or to change one’s decision.

In the sentence Vi har ombestemt oss, the reflexive seg changes to oss because the subject is vi.

Because å ombestemme seg is a reflexive verb in Norwegian.

That means it normally comes with a reflexive pronoun:

• jeg har ombestemt meg
• du har ombestemt deg
• han har ombestemt seg
• vi har ombestemt oss

English does not use a reflexive pronoun in the same way here. We usually say we have changed our minds, not we have changed ourselves. But in Norwegian, the reflexive pronoun is part of the normal structure of the verb.

It is the present perfect.

It is formed with:

• har = present tense of å ha
• ombestemt = past participle

So:

• Vi har ombestemt oss = We have changed our minds

This tense is used for something that happened in the past but is relevant now, or when the exact past time is not the main point.

In Norwegian, the perfect tense is usually made with ha.

So you get:

• har spist
• har kommet
• har bestemt
• har ombestemt oss

Unlike some other European languages, Norwegian does not switch to to be for verbs like this. So Vi er ombestemt oss would be wrong.

Because ombestemt is the past participle, and ombestemte is the simple past.

Compare:

• Vi ombestemte oss = We changed our minds
• Vi har ombestemt oss = We have changed our minds

So after har, you need the past participle:

• har ombestemt
• not har ombestemte

It changes the idea from simply deciding to deciding differently or changing a decision.

Compare:

• å bestemme = to decide
• å ombestemme seg = to change one’s mind

So om- is an important part of the meaning. Without it, the verb would not mean the same thing.

Normally, no.

For this meaning, å ombestemme seg is used with a reflexive pronoun, so oss should stay:

• Vi har ombestemt oss = correct

If you say just Vi har ombestemt, it sounds incomplete or unnatural in this meaning.

Both refer to changing one’s mind, but the tense is different.

• Vi har ombestemt oss = We have changed our minds

  • present perfect
  • often used when the result matters now

• Vi ombestemte oss = We changed our minds

  • simple past
  • often used when talking about a finished past event

A very common rough guide is:

• use har ombestemt oss when the present result matters
• use ombestemte oss when telling a past story or placing the action clearly in the past

It changes to match the subject.

Examples:

• Jeg har ombestemt meg
• Du har ombestemt deg
• Han har ombestemt seg
• Hun har ombestemt seg
• Vi har ombestemt oss
• Dere har ombestemt dere
• De har ombestemt seg

So in your sentence, oss is there because the subject is vi.

Like this:

• Vi har ikke ombestemt oss. = We have not changed our minds.
• Har vi ombestemt oss? = Have we changed our minds?

This shows two useful word-order patterns:

• In a normal statement, the finite verb comes early: Vi har ...
• With ikke, the negation usually comes after the finite verb: har ikke
• In a yes/no question, the finite verb comes first: Har vi ...?

Yes, å ombestemme seg is a very natural and common way to express this idea.

It is one of the standard ways to say change one’s mind in Norwegian. So Vi har ombestemt oss sounds normal and idiomatic.