Dnes večer ti chci napsat dopis.

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

Here, chci means I want, so the subject I is already built into the verb. You could say Já dnes večer ti chci napsat dopis, but já is usually unnecessary unless you want emphasis or contrast.

Dnes means today, and večer means evening. Together, dnes večer means this evening / tonight.

This is a very common Czech time expression. Czech often uses simple adverbial expressions like this without a preposition.

Ti is the dative form of ty and means to you / for you.

In this sentence, the verb idea is write a letter to someone, so Czech uses the dative for the person receiving the letter:

• napsat ti dopis = write you a letter / write a letter to you

By contrast:

• tě is usually accusative or genitive, not dative
• tebe is the stressed/full form, used for emphasis or after some prepositions

So ti is the normal unstressed form here.

Both are dative and both can mean to you, but they are used differently:

• ti = unstressed, normal everyday form
• tobě = stressed/emphatic form

So:

• Dnes večer ti chci napsat dopis. = neutral
• Dnes večer chci napsat dopis tobě. = emphasizes to you

English usually does this with stress in speech, but Czech can show it through the choice of form and word order.

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

• psát = imperfective, focuses on the process of writing
• napsat = perfective, focuses on completing the letter

In chci napsat dopis, the idea is I want to write a letter in the sense of get it written / complete it, so napsat is natural.

If you used psát, it would sound more like wanting to be engaged in the activity of writing, without emphasizing completion.

Dopis is in the accusative singular, because it is the direct object of napsat.

For this noun, the nominative and accusative singular are the same:

• nominative: dopis = a letter
• accusative: dopis = a letter as the object

So even though the form does not change, its grammatical role does.

Yes, Czech word order is flexible. The sentence given is natural, but other orders are also possible depending on emphasis.

For example:

• Dnes večer ti chci napsat dopis. = neutral, natural
• Dnes večer chci ti napsat dopis. = also possible, though often a bit less natural
• Dopis ti chci napsat dnes večer. = emphasizes the letter
• Tobě chci dnes večer napsat dopis. = emphasizes to you

Czech word order is influenced a lot by topic and focus: what is already known, and what is being highlighted.

Short unstressed pronouns like ti often appear in the second position area of the sentence or clause. These are often called clitics.

So Czech likes to place words like mi, ti, si, ho, mu near the beginning, after the first element if possible.

That is one reason Dnes večer ti chci napsat dopis sounds natural: after the opening time phrase, the short pronoun appears early.

Both are possible, but ti napsat is usually more natural in a neutral sentence.

Czech clitic pronouns like ti tend to come before the infinitive:

• chci ti napsat dopis = very natural
• chci napsat ti dopis = possible, but usually marked or less natural

So if you are unsure, chci ti napsat dopis is a safer pattern.

No, dnes večer is the normal fixed expression.

• dnes večer = this evening / tonight

Večer dnes would sound unusual in normal speech. Czech time expressions often have a preferred order, and this is one of them.

Yes, but the meaning changes.

• Dnes večer ti chci napsat dopis. = I want to write you a letter tonight
• Dnes večer ti budu chtít napsat dopis. = Tonight I will want to write you a letter, which is unusual in most contexts

Usually, if your present desire is about a future action, Czech simply uses the present tense of chtít plus the infinitive. So chci napsat is the normal choice.

Yes, chci is one of those forms learners often find tricky.

It is pronounced roughly like kh-tsi:

• ch = like the ch in German Bach or Scottish loch
• then c = ts
• then i

So the whole word is compact and consonant-heavy. In careful speech, it may sound almost like khci / khtsi, depending on the speaker.

It is informal, because of ti, which corresponds to you singular informal.

If you wanted to say this formally to one person, you would use Vám:

• Dnes večer Vám chci napsat dopis.

If speaking to several people informally, you would use vám as well, because plural you also takes that form in the dative.

Yes, but it means something different.

• napsat dopis = write a letter
• poslat dopis = send a letter

So if the meaning shown to the learner is about writing, napsat is correct. If the idea is mailing or sending it, then poslat would be used.

A useful way to break it down is:

• Dnes večer = time expression
• ti = indirect object in the dative, to you
• chci = finite verb, I want
• napsat = infinitive, to write
• dopis = direct object, a letter

So the structure is roughly:

[time] + [indirect object] + [want] + [infinitive] + [direct object]

A very common Czech pattern is:

• chci + infinitive
• dát/říct/napsat někomu něco = give/tell/write someone something