Napište své příjmení.

Napište is the imperative form of the verb napsat, meaning to write down / to write completely.

More specifically, it is the 2nd person plural imperative:

• napiš = write! (to one person informally)
• napište = write! (to several people, or to one person formally/politely)

So in this sentence, it functions as a command or instruction: Write ...

This is about aspect, which is very important in Czech.

• napsat is perfective: it focuses on the completed result
• psát is imperfective: it focuses on the process or ongoing action

So:

• Napište své příjmení. = Write down your surname / fill in your surname
• Pište... would sound more like be writing, write repeatedly, or it may fit a different context

On forms, signs, and instructions, Czech very often uses the perfective imperative, because the point is to complete the action.

Yes. Napište can be used:

• for more than one person
• or for one person formally/politely

So this sentence is appropriate in formal instructions, on forms, in offices, at reception desks, and so on.

If you were speaking to one friend informally, you would usually say:

Napiš své příjmení.

Because Czech often omits subject pronouns when they are clear from the verb form.

The ending -te in napište already tells you that the subject is:

• you plural
• or you formal singular

So adding vy is usually unnecessary unless you want emphasis or contrast.

No. In Czech, bare imperatives are very common in:

• instructions
• notices
• forms
• official prompts

So Napište své příjmení. is a normal, neutral instruction, not rude.

If someone wanted to make it sound more explicitly polite in conversation, they could say:

Prosím, napište své příjmení.

But on a form or screen prompt, leaving out prosím is completely standard.

Své is the form of the reflexive possessive adjective svůj, which means one's own.

Czech usually uses svůj when the possessor is the same as the subject of the sentence.

Here, the understood subject is you:

• (Vy) napište své příjmení.
• literally: Write your own surname

That is why své is the most natural choice.

Vaše příjmení is not impossible, but své příjmení is more standard here. Vaše can sound more contrastive, as if stressing your surname rather than someone else's.

Because svůj has to agree with příjmení in gender, number, and case.

Příjmení is:

• neuter
• singular
• here used as the direct object

So svůj becomes své.

You can think of it like this:

• base dictionary form: svůj
• neuter singular form here: své

Here příjmení is in the accusative singular, because it is the direct object of Napište.

You are writing what?
→ své příjmení

The reason it looks unchanged is that for this noun, the nominative and accusative singular have the same form:

• nominative: příjmení
• accusative: příjmení

That is very common with many Czech neuter nouns.

Yes. Both are possible:

• své příjmení
• svoje příjmení

In many situations they mean the same thing.

A rough tendency is:

• své = a bit shorter, often felt as slightly more formal or written
• svoje = often a bit more everyday or colloquial

In an instruction like this, své příjmení is very natural.

Because Czech does not have articles like English a/an and the.

So Czech simply says:

• Napište své příjmení.

and the meaning is understood from context.

In English, you need something like your surname. In Czech, definiteness is usually shown by context, word choice, and possession, not by articles.

Yes, Czech word order is flexible, but verb first is very common in commands and instructions.

So:

• Napište své příjmení. = neutral instruction

You could also say:

• Své příjmení napište.

But that sounds more marked, with extra emphasis on své příjmení. On a form or instruction sheet, the original order is the most natural.