In this pattern, aan die + infinitive works as a fixed construction. Here, die is part of the progressive expression, not the normal article the in the usual sense.
So it is best to learn aan die saai as one grammatical pattern meaning in the process of sowing.
You will see the same structure in many other sentences, for example:
Here saai is the infinitive / base verb form, not the main finite verb of the sentence.
The finite verb is was.
That is the verb carrying the tense.
So in:
the structure is roughly:
Also, even though saai can have other meanings in other contexts, here the grammar clearly shows it is being used as a verb.
Because after aan die, Afrikaans normally uses the bare infinitive, without te.
So you say:
not:
You do get te in other constructions, such as:
So:
Both are correct, but they use different grammar patterns.
The difference is mainly aspect:
Ons het gesaai = we sowed / we have sown
Ons was aan die saai = we were sowing
So if you want to emphasize that the activity was in progress, aan die is the better choice.
Yes. That is a very natural alternative.
Both sentences can mean nearly the same thing:
A rough difference is:
In everyday Afrikaans, both are common.
Mostly, you use it with action verbs that can really be seen as ongoing activities.
Good fits are verbs like:
It is less natural with strongly stative verbs such as verbs meaning know, believe, or own, because those are not usually thought of as active ongoing processes.
So aan die is best learned as a progressive pattern for actions in progress.
Yes. It is complete if the context already makes that clear.
Afrikaans, like English, often leaves out information that the listener already knows. So Ons was aan die saai is fine on its own if everyone understands what activity is being discussed.
If needed, you can add more detail, for example a place, time, or object.