Learn Hardcore Czech: Můj syn nikdy nenosí sluchátka.

This applies to all negative words: nikdo (nobody), nic (nothing), nikdy (never), nikde (nowhere), etc. The verb must also take ne-:

Nikdo mě nezná. – Nobody knows me.
Nikdy tam nechodím. – I never go there.

Why is the verb nosí used here and not something like má (“has”) or používá (“uses”)?

Czech has specific verbs for “wearing” things:

nosit – to wear something (habitually, repeatedly)
mít na sobě – to have something on (right now, at this moment)

In this sentence:

nenosí is from nosit, so it means he doesn’t (habitually) wear.

So:

Můj syn nikdy nenosí sluchátka.
= He never wears headphones (as a habit, in general).

If you said:

Můj syn nikdy nemá sluchátka na uších.
= My son never has headphones on (on his ears) – more specific to the physical situation.

používat (to use) would sound more like “My son never uses headphones”, which focuses on use rather than wearing, but it’s understandable:

Můj syn nikdy nepoužívá sluchátka. – also possible, slightly different nuance.

What exactly is the verb form nosí? How does it fit into the conjugation?

Nosí is the 3rd person singular present tense of the verb nosit (imperfective, “to wear regularly / to carry repeatedly”).

Present tense conjugation of nosit:

já nosím – I wear
ty nosíš – you wear (sg., informal)
on/ona/ono nosí – he/she/it wears
my nosíme – we wear
vy nosíte – you wear (pl. or formal)
oni nosí – they wear

So nenosí = he doesn’t wear (or they don’t wear – the 3rd person singular and plural look the same; you see which one it is from context).

Why is it sluchátka and not some other form of the word? Which case is it?

Sluchátka is the accusative plural form of sluchátko (a small listening device, earphone/headphone).

Patterns:

Nominative sg.: sluchátko
Nominative pl.: sluchátka
Accusative sg.: sluchátko
Accusative pl.: sluchátka

For neuter nouns like sluchátko, the nominative and accusative look the same in both singular and plural. In this sentence, sluchátka is the direct object of the verb (ne)nosí, so it’s in the accusative plural.

Why is sluchátka plural in Czech? Can you say it in singular?

You can use the singular sluchátko, but:

In everyday speech, sluchátka is normally used in the plural for “headphones” or “earphones” as a pair.
Singular sluchátko is usually used when you mean one piece (for example, one earbud from a pair, or a single earpiece).

So:

Můj syn nikdy nenosí sluchátka. – My son never wears headphones (natural).
Můj syn nikdy nenosí sluchátko. – Sounds like “He never wears a single earpiece” – unusual unless context is special.

Why is there no word for “a” or “the” in this sentence? How do you know if it’s “the headphones” or “headphones in general”?

Czech does not have articles (no “a/an/the”). The sentence:

Můj syn nikdy nenosí sluchátka.

can mean, depending on context:

My son never wears headphones.
My son never wears any headphones.
My son never wears the headphones.

Czech relies on:

context,
word order,
sometimes extra words (like ty = “those”, tahle = “these”),

to express what English does with “a” vs. “the”.

If you really want to emphasize “any at all”, you can add žádná:

Můj syn nikdy nenosí žádná sluchátka. – My son never wears any headphones.

Could the word order be Nikdy můj syn nenosí sluchátka or Můj syn nenosí nikdy sluchátka?

Word order in Czech is more flexible than in English, but some orders are more natural than others.

The most natural here is:

Můj syn nikdy nenosí sluchátka.

Other options:

Nikdy můj syn nenosí sluchátka.
– Grammatically possible, but sounds emphatic or unusual, focusing strongly on nikdy at the beginning, and “můj syn” as a kind of contrast:
Never (ever) does my son wear headphones.
Můj syn nenosí nikdy sluchátka.
– Understandable, but less natural; Czech usually puts nikdy before the verb it negates.
Sluchátka můj syn nikdy nenosí.
– Also possible, and emphasizes “headphones” (as opposed to some other thing).

For a neutral, everyday statement, Můj syn nikdy nenosí sluchátka is best.

What is the difference between nikdy and vůbec? Could I say Můj syn vůbec nenosí sluchátka?

nikdy = never (concerns time, frequency)
vůbec = (not) at all, absolutely not (concerns degree, emphasis)

So:

Můj syn nikdy nenosí sluchátka.
– My son never wears headphones (at no time).
Můj syn vůbec nenosí sluchátka.
– My son doesn’t wear headphones at all / He simply does not wear headphones.

You can combine them for extra emphasis:

Můj syn nikdy vůbec nenosí sluchátka.
– Very strong: He absolutely never ever wears headphones (quite emphatic).

Why is it můj syn and not moje syn? What’s the rule for můj / moje / mojeho etc.?

The possessive pronoun “my” changes form based on the gender and case of the noun.

For můj in the nominative singular:

můj – with masculine nouns (animate & inanimate):
- můj syn – my son
- můj dům – my house
moje – with feminine and neuter nouns:
- moje matka – my mother
- moje auto – my car

In the sentence, syn is masculine, nominative singular (subject), so we use můj syn.

Other cases change more (e.g. mého syna, mého syna, etc.), but in this sentence it’s the simple nominative form: můj.

How would I say “My sons never wear headphones” in Czech? Does anything except syn change?

You need to make syn plural and adjust the verb:

Mí synové nikdy nenosí sluchátka.
– My sons never wear headphones.

Changes:

Můj syn → Mí synové
- můj → mí (masculine personal plural)
- syn → synové (plural nominative)

The verb form nenosí stays the same, because:

3rd person singular and plural of nosit in present tense are identical:
- on (ne)nosí – he (doesn’t) wear(s)
- oni (ne)nosí – they (don’t) wear

You understand singular vs. plural from context and the subject noun (syn vs synové).