Δεν έχω τίποτα να δηλώσω, αλλά έχω κάτι να αγοράσω πριν από την επιβίβαση.

Yes, literally it looks like a double negative: δεν = not, and τίποτα = nothing / anything.

But in Greek, this is completely normal. Greek commonly uses negative concord, which means the negative word and the negative particle appear together:

• Δεν έχω τίποτα = I have nothing
• literally: I don’t have nothing

In standard Greek, you usually need δεν with verbs in negative sentences like this. So this is not a mistake or bad grammar; it is the normal Greek pattern.

They are opposite indefinite pronouns:

• τίποτα = nothing / anything
• κάτι = something

So:

• Δεν έχω τίποτα να δηλώσω = I have nothing to declare
• Έχω κάτι να αγοράσω = I have something to buy

Notice the contrast in the sentence:

• first clause: nothing to declare
• second clause: something to buy

That contrast is one reason αλλά (but) fits naturally here.

Modern Greek does not use the infinitive the way English does.

English says:

• to declare
• to buy

Greek usually expresses this idea with να + subjunctive form:

• να δηλώσω
• να αγοράσω

So the structure:

• τίποτα να δηλώσω
• κάτι να αγοράσω

corresponds to English:

• nothing to declare
• something to buy

This is one of the most important differences between English and Greek grammar: where English often uses an infinitive, Greek often uses να plus a finite verb form.

They are aorist subjunctive, first person singular.

Breakdown:

• δηλώσω = that I declare / to declare
• αγοράσω = that I buy / to buy

More precisely, after να, these are subjunctive forms based on the aorist stem.

Why the aorist? Because here the action is seen as a single whole event:

• declare something
• buy something

This is very common after να when talking about a complete action rather than an ongoing process.

Compare the general idea:

• να αγοράζω would suggest repeated or ongoing buying
• να αγοράσω suggests one completed act of buying

In this sentence, the aorist is the natural choice.

The Greek structure with έχω + something/nothing + να + verb often means:

• I have something to...
• I have nothing to...

So:

• Έχω κάτι να αγοράσω = I have something to buy
• Δεν έχω τίποτα να δηλώσω = I have nothing to declare

Sometimes έχω να + verb can also express obligation or something pending, like I have to..., but in this sentence the presence of κάτι and τίποτα makes the meaning very clearly:

• there is something/nothing that I need or intend to do

So the English translation I have something to buy is the best match.

Αλλά means but.

It connects two contrasting ideas:

• Δεν έχω τίποτα να δηλώσω = I have nothing to declare
• αλλά έχω κάτι να αγοράσω = but I have something to buy

So the sentence contrasts:

• no customs declaration
• yes, a shopping intention before boarding

This is a very standard use of αλλά.

Πριν από means before when it is followed by a noun phrase.

Here it is followed by:

• την επιβίβαση = the boarding

So:

• πριν από την επιβίβαση = before boarding / before the boarding process

In Greek:

• πριν από + noun = before + noun
• πριν (να) + verb/clause = before + verb/clause

For example:

• πριν από την επιβίβαση = before boarding
• πριν επιβιβαστώ or πριν να επιβιβαστώ = before I board

So in this sentence, because the next word is a noun, πριν από is the natural form.

Greek often uses the definite article in places where English does not.

So Greek says:

• την επιβίβαση = literally the boarding

But in natural English, we often translate this more smoothly as:

• before boarding

The noun επιβίβαση means boarding. In this context, it refers to the specific boarding event relevant to the speaker, so the article is perfectly natural in Greek.

This is a very common difference between the two languages: Greek uses the article more often than English.

It is in the accusative singular.

Why? Because από is a preposition that takes the accusative, and in the phrase πριν από, the noun that follows is also in the accusative.

So:

• η επιβίβαση = nominative
• την επιβίβαση = accusative

You can see the feminine singular article change:

• η → nominative
• την → accusative

This is standard Greek case usage after prepositions like από.

Yes, Greek word order is more flexible than English word order.

The sentence as given is completely natural:

• Δεν έχω τίποτα να δηλώσω, αλλά έχω κάτι να αγοράσω πριν από την επιβίβαση.

But Greek could shift things around for emphasis. For example, you might hear:

• Πριν από την επιβίβαση, έχω κάτι να αγοράσω.

That gives more emphasis to the time phrase before boarding.

However, in the original sentence, the order is straightforward and neutral:

1. first statement
2. contrast with αλλά
3. second statement
4. time phrase at the end

That makes it easy to understand.

Yes, very much.

Δηλώνω means declare. In travel contexts, especially airports or customs, έχω κάτι να δηλώσω means:

• I have something to declare

So:

• Δεν έχω τίποτα να δηλώσω is exactly the kind of sentence you might use at customs.

It is a very practical travel phrase. In fact, many learners encounter this structure early because it is so common in airport and border situations.

It is understandable and grammatically correct, and it sounds like practical travel-related Greek.

The first half:

• Δεν έχω τίποτα να δηλώσω

is especially natural and common.

The second half:

• αλλά έχω κάτι να αγοράσω πριν από την επιβίβαση

is also correct and natural enough, though in everyday speech someone might choose a slightly simpler alternative depending on context, such as:

• ...αλλά θέλω να αγοράσω κάτι πριν από την επιβίβαση.
• ...αλλά πρέπει να αγοράσω κάτι πριν από την επιβίβαση.

Those would mean slightly different things:

• θέλω = I want
• πρέπει = I need / must

But your original sentence is perfectly good Greek and clearly means that there is something the speaker intends or needs to buy before boarding.