není / nejsou

The verb být (to be) is the most common verb in Czech. To negate almost any Czech verb, you simply attach the prefix ne- to the front (as seen in slovesná negace ne-).

However, the 3rd-person singular form is a major exception:

• je (is) ➔ není (is not) — Never say "neje"!
• jsou (are) ➔ nejsou (are not) — Perfectly regular.

The rest of the negative paradigm (nejsem, nejsi, nejsme, nejste) is also completely regular. Also, remember that subject pronouns (já, ty, on/ona/to) are usually dropped in Czech because the verb form itself already indicates the person. Note that nejsi is strictly for the informal singular "you", while nejste must be used for the formal singular "you" (vykání). Furthermore, the past (e.g., nebyl, which must agree with gender and number, such as nebyla or nebylo) and future (nebudu) negative forms of 'být' are completely regular too. Note: While nejsi is the standard 2nd-person singular negative, in everyday spoken Czech you will constantly hear the colloquial form nejseš (which comes from the colloquial positive form seš, replacing jsi). Similarly, in everyday speech, the long 'í' in není is almost always shortened to neni.

Key Rules to Remember:

1. One word, stressed on the first syllable: The ne- is glued to the verb. Pronounce them as NE-ní and NE-jsou. Because the ne- prefix carries the stress, all negative forms of the verb (nejsem, není, nejsou) can comfortably start a sentence. Unlike the positive forms (jsem, jsi, jsme, jste), which are unstressed clitics that must go in the second position (note that positive je and jsou are not strict clitics and can take stress to start a sentence, e.g., Je to dobré), negative forms are fully independent words. Additionally, while the 'j' in positive forms (like jsem or jsi) is traditionally pronounced in standard speech when acting as the main verb, it is usually silent when used as an unstressed past-tense auxiliary or in colloquial speech. However, it is always clearly pronounced in the negative forms (nejsem, nejsou).

2. Existential meaning: To say "There is no problem," just say Není problém. Do not add the word tam (there), which refers to a physical location ("over there"). When using this subjectless existential construction in the past or future tense, it defaults to the neuter singular form (nebylo, nebude). In formal or literary Czech, you may encounter the Genitive of Negation (genitiv záporový knižní), where the negated existential verb takes a genitive subject instead of nominative (e.g., Není času, Není peněz). This survives in everyday speech in extremely common fixed phrases like Není divu (No wonder), Není pochyb (There is no doubt), and Není zač (You're welcome / Not at all).

3. Double negatives: Czech grammatically requires multiple negatives. If you use a negative pronoun like nikdo (nobody), you must also negate the verb: Nikdo tady není (literally: "Nobody isn't here").