Anna zet haar tas stevig op de fiets vast voordat zij vertrekt.

Because the full verb is vastzetten, which is a separable verb.

• Infinitive: vastzetten = to fasten, secure
• Main clause: Anna zet ... vast
• Subordinate clause / infinitive: the parts stay together, for example om haar tas vast te zetten

This is very common in Dutch:

• opbellen → Ik bel je morgen op
• meenemen → Zij neemt haar tas mee
• vastzetten → Anna zet haar tas vast

So zet ... vast is not two separate ideas; it is one verb split by normal Dutch word order.

Here vastzetten means to fasten, to secure, or to tie/attach firmly so it won’t move.

In this sentence, Anna is making sure the bag is securely attached to the bicycle before she leaves.

A related verb you may also hear is vastmaken, which can mean almost the same thing in everyday Dutch:

• Anna maakt haar tas vast
• Anna zet haar tas vast

Both can work, though vastzetten can sound a bit more like securing something in place.

Dutch main clauses usually put the finite verb in the second position. That is the key rule here.

So the structure is:

• Anna = subject
• zet = finite verb, in second position
• haar tas = object
• stevig = adverb
• op de fiets = prepositional phrase
• vast = separable particle belonging to vastzetten

So even though English might prefer something like Anna securely fastens her bag to the bicycle, Dutch keeps zet early and pushes the separable part vast toward the end.

Stevig here means firmly, securely, or tightly.

It describes how Anna fastens the bag. The idea is that she does not attach it loosely; she makes sure it is fixed well.

Depending on context, stevig can also mean:

• firm
• sturdy
• solid
• strong

But in this sentence, the adverb meaning securely/firmly is the natural one.

Op de fiets is natural here because the bag is understood as being secured on the bicycle—for example on a luggage rack, over the back, or otherwise positioned on it.

Dutch often uses:

• op de fiets = on the bike
• in de auto = in the car
• op tafel = on the table

You may also hear aan de fiets in other contexts, especially when something is attached to the side or frame. But in this sentence, op de fiets vastzetten is a normal way to express securing the bag on the bike.

So the choice is partly about Dutch idiom, not just literal one-to-one translation from English.

Haar means her.

Since Anna is female, the possessive adjective is haar:

• haar tas = her bag

Compare:

• zijn tas = his bag
• mijn tas = my bag
• jouw tas = your bag

So haar matches the owner, Anna.

Both zij and ze can mean she.

• zij is the fuller form
• ze is the unstressed, more common everyday form

So you could also say:

• ... voordat ze vertrekt

That would sound very natural too.

Why use zij here?

• It can sound a little more formal or careful.
• It may give slightly more emphasis to the subject.
• In written Dutch, the full form often appears more than in casual speech.

So this is not a big grammar difference; it is mostly about style and emphasis.

Because voordat introduces a subordinate clause, and in Dutch subordinate clauses the verb usually goes to the end.

Compare:

Main clause

• Anna vertrekt.

Subordinate clause

• voordat zij vertrekt

This is a very important Dutch pattern:

• omdat zij moe is
• als hij komt
• voordat zij vertrekt
• terwijl ik werk

So once you see a subordinating conjunction like voordat, expect the verb to move to the end of that clause.

Dutch often uses the present tense to talk about the near future, just like English sometimes does.

So:

• Anna vertrekt can mean Anna leaves or Anna is leaving
• In this context, it clearly means something that happens shortly afterward

Because the sentence already includes voordat and the context is clear, Dutch does not need a special future form here.

You could make the future more explicit, but it is usually unnecessary:

• voordat zij zal vertrekken is possible in some contexts, but much less natural here

So the simple present is the normal choice.

Yes. Voordat ze weggaat is a very natural alternative.

There is a small difference in feel:

• vertrekken = to depart, to leave; slightly more formal or neutral
• weggaan = to go away, leave; a bit more everyday

So these are both possible:

• Anna zet haar tas stevig op de fiets vast voordat zij vertrekt.
• Anna zet haar tas stevig op de fiets vast voordat ze weggaat.

The original sentence sounds a little more polished or written.

Literally, de fiets means the bicycle.

But in context, Dutch often does not repeat possession if it is obvious. So listeners will usually understand that it is probably her bike, even though the sentence only says the bike.

This is normal in Dutch and in English too:

• She washed the car may clearly mean her car
• Hij doet de jas aan often means he puts on his coat

So de fiets is grammatically just the bicycle, but context may strongly suggest it is Anna’s bicycle.

Yes, Dutch word order is flexible in some parts of the sentence, though some versions sound more natural than others.

For example, these are possible:

• Anna zet haar tas stevig op de fiets vast.
• Anna zet haar tas op de fiets stevig vast.

The first version is more natural for most speakers.

What usually stays the same:

• the finite verb zet stays in second position in the main clause
• the separable part vast stays near the end
• in the subordinate clause, vertrekt stays at the end

So Dutch allows some movement, but not total freedom.

The infinitive is vastzetten.

So if you wanted to refer to the action in a dictionary-style or learner-style way, you would say:

• Anna wil haar tas stevig op de fiets vastzetten.
• Het is belangrijk om je tas goed vast te zetten.

Notice the difference:

• In a main clause with a finite verb: zet ... vast
• In the infinitive: vastzetten

That is the standard behavior of a separable verb.