Czy mówisz poważnie, czy tylko żartujesz?

The first czy is a question particle. It is commonly used to introduce a yes/no question in Polish.

So:

• Czy mówisz poważnie? = Are you serious? / Do you mean that seriously?

In everyday speech, Polish often drops this first czy, so you may also hear:

• Mówisz poważnie?

That sounds natural and conversational.

The two czy words do different jobs here.

• The first czy introduces the whole question.
• The second czy means or in a choice between two possibilities.

So the structure is basically:

• Czy X, czy Y? = Is it X, or is it Y?

In this sentence:

• Czy mówisz poważnie, czy tylko żartujesz?
• Are you serious, or are you just joking?

This repetition is normal in Polish.

Polish often expresses this idea with the verb mówić (to speak / to say) plus the adverb poważnie (seriously).

So:

• mówić poważnie = to speak seriously, but in context it often means to be serious or to mean something seriously

That is why Czy mówisz poważnie? is a very natural way to say:

• Are you serious?
• Do you mean it seriously?

A more colloquial alternative is:

• Serio? = Seriously?
• Mówisz serio? = Are you serious?

Poważnie is an adverb, not an adjective.

• poważny = serious (adjective)
• poważnie = seriously (adverb)

Because it modifies the verb mówisz (you speak / you mean), Polish uses the adverb:

• mówisz poważnie = you’re speaking seriously / you mean it seriously

You would not use poważny here, because that adjective would need to describe a noun or a person in a different sentence structure.

Both are:

• 2nd person singular
• present tense
• informal
• used with ty = you

So:

• mówisz = you speak / you say / you mean
• żartujesz = you joke / you are joking

In context, English translates them naturally as:

• Are you serious, or are you just joking?

Even though Polish uses the present tense forms directly, the meaning matches normal English present progressive very well here.

Because in Polish, the verb ending already shows who the subject is.

• mówisz already means you say / you mean
• żartujesz already means you joke

So ty is usually omitted unless you want emphasis or contrast.

For example:

• Czy ty mówisz poważnie? = Are you seriously saying that? / You’re serious?

Adding ty can sound more emphatic, surprised, or emotionally charged.

Tylko usually means only, just, or merely.

Here it softens the second option:

• czy tylko żartujesz = or are you just joking

So the sentence contrasts:

• you mean it seriously with
• you’re only joking

This is a very natural use of tylko in Polish.

It is informal singular, because mówisz and żartujesz are forms used with ty.

You would say this to:

• a friend
• a sibling
• someone your age in an informal situation

If you want to be formal, you would say for example:

• Czy mówi pan poważnie, czy tylko pan żartuje?
  (to a man)

• Czy mówi pani poważnie, czy tylko pani żartuje?
  (to a woman)

A gender-neutral polite plural version would be:

• Czy mówią państwo poważnie, czy tylko państwo żartują?

Yes. Polish word order is fairly flexible, and small changes can affect tone more than basic meaning.

For example:

• Czy mówisz poważnie, czy tylko żartujesz?
  slightly more neutral and textbook-like

• Mówisz poważnie, czy tylko żartujesz?
  very natural in everyday speech

• Czy ty mówisz poważnie, czy tylko żartujesz?
  more emphatic, often showing surprise

So the version with the first czy is completely correct, but in conversation people often drop it.

Because the second czy introduces the second part of an either/or contrast.

So the sentence naturally splits into two alternatives:

• Czy mówisz poważnie,
• czy tylko żartujesz?

The comma helps show that contrast clearly. In standard written Polish, this punctuation is correct.

A rough pronunciation guide is:

• Czy ≈ chi
• mówisz ≈ MOO-vish
• poważnie ≈ po-VAZH-nye
• czy ≈ chi
• tylko ≈ TIL-ko
• żartujesz ≈ zhar-TOO-yesh

A smoother full version:

• chi MOO-vish po-VAZH-nye, chi TIL-ko zhar-TOO-yesh?

A few helpful sound notes:

• czy has a ch-like sound, but harder than English ch
• ż sounds like the s in measure
• rz and ż usually sound the same in modern Polish
• ni in poważnie gives a soft ny sound

Yes. Depending on tone, Polish speakers might also say:

• Mówisz serio, czy żartujesz? = Are you serious, or are you joking?
• Serio czy żartujesz? = Seriously, or are you joking?
• Na serio, czy żartujesz? = Seriously, or are you joking?

Your original sentence is perfectly natural, but these alternatives may sound a bit more casual in everyday conversation.