moci

1. Conjugation (Everyday vs. Formal)
Czech has two sets of forms for "I can" and "they can".

• Everyday/Spoken: můžu (I can), můžou (they can). The infinitive is moct. These are perfectly correct for normal conversation and informal writing!
• Formal/Written: mohu (I can), mohou (they can). The infinitive is moci. You will see these in official texts or hear them in very polite situations (like a shop assistant talking to a customer).

The other forms are identical in both registers: můžeš (you can), může (he/she can), můžeme (we can), můžete (you can - plural/formal).

2. How to use it in a sentence
Like in English, moci attaches directly to the infinitive without any linking words.
Example: Můžu jít. (I can go.)

3. When to use moci (Ability and Permission)
Use moci for circumstantial ability (e.g., I can swim today because the pool is open) and for asking or granting permission in everyday speech (e.g., Můžu se zeptat? - Can I ask?). This is a crucial distinction from umět, which is used for learned skills (e.g., I know how to swim). For formal or strict permission, Czech uses a dedicated verb, smět (to be allowed to).

4. Negation
To say "cannot" (lack of ability or possibility), simply add the ne- prefix: nemůžu, nemůžeš, etc. Note that to express strict prohibition ("must not" or "may not"), you should use the verb nesmět.

5. Verbs of Perception
Unlike English, Czech does not use moci with verbs of perception like seeing or hearing. Instead of saying "I can see you", you simply use the base verb: Vidím tě (I see you).

6. Other Common Uses
In everyday speech, moci is often used on its own without an infinitive to express physical exhaustion or being full: Já už nemůžu! (I can't take it anymore! / I'm full!). You will also frequently see it used with the reflexive pronoun se to express possibility: To se může stát. (That can happen.)