Learn Hardcore Czech: Dnes jsem unavený, nechci jít do parku. - Today I am tired, I don't want to go to the park.

Dnes jsem unavený – neutral, very common; puts light emphasis on today as the setting.
Jsem dnes unavený – also correct, slightly more neutral/emphatic on being tired rather than on today.
Jsem unavený dnes – grammatically possible, but sounds more marked/contrasty, like “I’m tired today (but not usually)” and would need the right context.

So the sentence starts with Dnes simply as a natural, neutral way to set the time frame; it’s not the only correct option, but it’s the most typical one here.

Why is there no já (I) in Dnes jsem unavený? Would Já jsem unavený be wrong?

Czech is a pro‑drop language: subject pronouns (já, ty, on, ona etc.) are usually omitted because the verb ending already shows who the subject is.

Jsem unavený – clearly “I am tired” from the form jsem.
Já jsem unavený – also correct, but you normally use já only for emphasis or contrast, like:
- Já jsem unavený, ale ty ne. – I’m tired, but you aren’t.

So Já jsem unavený isn’t wrong; it just sounds more emphatic than needed in a simple statement.

Why is it unavený and not something like unavená or unavené?

The adjective unavený (tired) agrees in gender and number with the subject:

Já jsem unavený. – a man speaking (masculine singular).
Já jsem unavená. – a woman speaking (feminine singular).
To dítě je unavené. – The child is tired (neuter singular).
My jsme unavení. – We (mixed group/men) are tired.
My jsme unavené. – We (all women) are tired.

In your sentence the speaker is assumed to be male, so unavený is used. A female speaker would say:

Dnes jsem unavená, nechci jít do parku.

Why is the verb jsem in the middle: Dnes jsem unavený? Could I say Dnes unavený jsem?

Dnes unavený jsem is technically possible but very marked and poetic, like Yoda-style English (“Today tired I am”). It’s not normal everyday speech.

The usual patterns are:

Dnes jsem unavený. – very natural.
Jsem dnes unavený. – also fine.
Jsem unavený dnes. – possible, but context-dependent and a bit emphatic on today.

Czech allows movement of elements for emphasis or style, but [time] + jsem + [adjective] is the normal, neutral order here.

Why is it nechci instead of something like já nechci or ne chci?

No “já”: As with jsem, you don’t need já because the verb ending in nechci already tells you it’s I (1st person singular).
One word, not two: Negation in Czech is usually formed by adding the prefix ne‑ directly to the verb:

chci – I want
nechci – I don’t want
mám – I have
nemám – I don’t have
rozumím – I understand
nerozumím – I don’t understand

You never write it as ne chci.

How is chtít → nechci conjugated? The stem seems to change a lot.

The verb chtít (to want) is irregular. In the present tense:

já chci / nechci – I want / I don’t want
ty chceš / nechceš – you want
on/ona/ono chce / nechce – he/she/it wants
my chceme / nechceme – we want
vy chcete / nechcete – you (pl./formal) want
oni chtějí / nechtějí – they want

The changes cht → chci / chce are part of the irregularity. You just have to learn the pattern.

Why is it nechci jít do parku and not just nechci do parku?

In Czech, chtít (“to want”) almost always needs either:

An infinitive verb:
- Nechci jít do parku. – I don’t want to go to the park.
- Chci spát. – I want to sleep.
Or a noun phrase, but then the meaning is “want (to have / to get) something”:
- Chci kávu. – I want a coffee (to drink / to have).

In your sentence, you’re refusing the action of going, not the park itself, so you need the infinitive:

Nechci jít do parku. – I don’t want to go to the park.

Nechci do parku sounds incomplete or ungrammatical in standard Czech.

Why is it jít do parku and not jet do parku or chodit do parku?

Czech distinguishes several motion verbs:

jít – to go on foot, one specific movement.
jet – to go by vehicle (car, bus, train, etc.), one specific movement.
chodit – to go on foot regularly or repeatedly (habit).
jezdit – to go by vehicle regularly or repeatedly.

So:

Nechci jít do parku. – I don’t want to go to the park (on foot, now/this time).
Nechci jet do parku. – I don’t want to go to the park (by car/bus etc.).
Nechci chodit do parku. – I don’t want to go to the park regularly/as a habit.

The original sentence assumes walking there this time, so jít is used.

Why do we say do parku and not do park or do parka?

The preposition do (“to, into”) always requires the genitive case.

The noun park (a park) is masculine inanimate, and its genitive singular is parku:

nominative: park – ten park (the park)
genitive: parku – do parku (to the park), z parku (from the park)

So:

do parku – correct (preposition do
- genitive).
do park / do parka – incorrect forms for standard Czech.

Could I say na park instead of do parku? What’s the difference between do and na here?

Both do and na can express movement “to” a place, but with different typical uses:

do + genitive – going into an enclosed or defined space:
- do parku, do školy, do města – to the park, to school, to the city.
na + accusative – going onto a surface or to an event/activity:
- na stůl – onto the table
- na koncert – to a concert
- na stadion – to the stadium

For park, the natural collocation is do parku, because you are going into that area. Na park would usually sound wrong unless you meant literally onto some elevated construction called “park,” which is not the usual meaning.

Why is there a comma: Dnes jsem unavený, nechci jít do parku? Would English also have a comma there?

Czech punctuation is a bit stricter than English in this case.

You have two independent clauses:

Dnes jsem unavený. – Today I am tired.
Nechci jít do parku. – I don’t want to go to the park.

They are simply joined into one sentence, and Czech normally requires a comma between such clauses:

Dnes jsem unavený, nechci jít do parku.

In English, you might write:

Today I’m tired, I don’t want to go to the park. (comma splice; not ideal)
More naturally: Today I’m tired, so I don’t want to go to the park. or two sentences.

So the comma in Czech is obligatory here, even though English would more often use a conjunction or split into two sentences.

How do you pronounce tricky parts like dnes jsem and nechci?

Some notes on pronunciation:

dnes – usually [dnes]. The d is pronounced, but the cluster is quite fast. In casual speech, people often say dneska [ˈdneska] instead, which is a bit easier.
jsem – often pronounced [sem] in fluent speech; the initial j is weak or disappears. So dnes jsem commonly sounds like [dnes sem].
chci – [xt͡sɪ] or [xt͡si]. The ch is like German Bach, a voiceless velar fricative, and c is [ts].
nechci – [ˈnɛxt͡sɪ]; same chci cluster, just with ne‑ in front.
jít – [jiːt], with a long í.
parku – [ˈparkʊ], both consonants r and k clearly pronounced.

So in natural speech, the whole sentence might sound roughly like:

[dnes sem ʊˈnavɛniː nɛxt͡sɪ jiːt dɔ ˈparkʊ] (male speaker).

Is Dneska jsem unavený also correct, or must it be Dnes?

Yes, Dneska is perfectly correct and very common in everyday speech:

Dnes jsem unavený. – a bit more neutral/formal.
Dneska jsem unavený. – more colloquial/conversational.

They both mean today; the difference is mainly in style, not in grammar or meaning.