Ek het die orkes op die verhoog sien optree.

Afrikaans usually does not use a simple past the way English does in ordinary speech. Instead, it normally uses het plus another verb form to talk about past actions.

So where English says:

• I saw the orchestra perform

Afrikaans commonly says:

• Ek het die orkes ... sien optree

The word het is the past auxiliary here, roughly like have in structure, even though in English we translate the whole sentence as a simple past.

This is a very common learner question.

In Afrikaans, after verbs of perception such as sien (see) and hoor (hear), when there is another verb after them, Afrikaans often uses a double infinitive construction.

So you get:

• Ek het hom sien hardloop. = I saw him run.
• Ek het die orkes sien optree. = I saw the orchestra perform.

Not:

• Ek het hom gesien hardloop in the standard pattern meant here
• Ek het die orkes gesien optree
• Ek het die orkes sien opgetree

A useful contrast is:

• Ek het die orkes gesien. = I saw the orchestra.
  Here gesien is normal, because there is no second verb.
• Ek het die orkes sien optree. = I saw the orchestra perform.
  Here sien stays in the infinitive because it is part of the verb cluster with optree.

Afrikaans often puts the finite verb in second position in a main clause, and then the other verbs go toward the end.

So the structure here is:

• Ek = subject
• het = finite verb in second position
• die orkes = object
• op die verhoog = prepositional phrase
• sien optree = verb cluster at the end

That final position for the non-finite verbs is very normal in Afrikaans.

Op die verhoog means on the stage.

It is a prepositional phrase:

• op = on
• die verhoog = the stage

It tells you where the performing happened, or where the orchestra was when the speaker saw them perform.

So:

• Ek het die orkes op die verhoog sien optree
  = I saw the orchestra perform on the stage.

Yes, Afrikaans often allows some flexibility with adverbials and prepositional phrases.

For example, this can also be natural:

• Ek het die orkes sien optree op die verhoog.

Both versions are understandable. The original sentence is very natural, though, and places the location phrase before the final verbs.

A learner should mainly remember this pattern:

• Ek het + object + other information + verb(s) at the end

Yes. In Afrikaans, die is the definite article for:

• singular nouns
• plural nouns

So die can mean the in either number.

Examples:

• die man = the man
• die mans = the men
• die orkes = the orchestra
• die orkeste = the orchestras

Unlike English, Afrikaans does not have different forms of the for singular and plural.

Here it is singular: the orchestra.

The noun itself tells you that:

• orkes = orchestra
• orkeste = orchestras

Because die is used for both singular and plural, you cannot rely on the article alone to tell the number. You have to look at the noun form.

Optree is a verb meaning perform, appear on stage, or sometimes act/behave, depending on context.

It is one of those verbs that can behave like a separable verb. When it is in the infinitive or at the end of the clause, it is usually written as one word:

• om op te tree
• sien optree

But when the verb is the main finite verb in a main clause, it often splits:

• Die orkes tree op. = The orchestra is performing.

So:

• optree at the end / infinitive form
• tree op when conjugated in a main clause

That is completely normal.

They are two forms of the same verb.

Compare:

• Die orkes tree vanaand op.
  = The orchestra is performing tonight.

• Ek wil die orkes sien optree.
  = I want to see the orchestra perform.

• Ek het die orkes sien optree.
  = I saw the orchestra perform.

So if the verb is in its infinitive/final form, it appears as optree. If it is the conjugated main verb in a main clause, the parts often separate: tree ... op.

Because this is not an om ... te infinitive construction.

After a perception verb like sien, Afrikaans normally uses a bare infinitive:

• Ek het hom sien kom.
• Ek het hulle hoor sing.
• Ek het die orkes sien optree.

You would not normally say:

• Ek het die orkes sien om op te tree
  for this meaning.

So after sien in this structure, just use the verb directly.

Afrikaans normally uses double negation:

• Ek het die orkes nie op die verhoog sien optree nie.

The pattern is:

• first nie after the part being negated
• second nie at the end of the clause

So for learners, a safe model is:

• Ek het ... nie ... nie.

Yes, but it means something slightly simpler:

• Ek het die orkes gesien. = I saw the orchestra.
• Ek het die orkes sien optree. = I saw the orchestra perform.

The second sentence is more specific because it says what you saw them doing.

So:

• gesien = saw them / noticed them
• sien optree = saw them performing

Yes, it is very natural.

A native speaker would understand it immediately, and it follows a very common Afrikaans pattern:

• Ek het + object + place/time/etc. + sien/hoor + main verb

For example:

• Ek het die kinders buite hoor speel.
• Ek het haar in die straat sien loop.
• Ek het die orkes op die verhoog sien optree.

So this sentence is a very useful model to learn from.