German splits "not" into two words depending on what's being negated - a noun with an indefinite/no article, or everything else. Pick the wrong one and you'll still be understood, but it's one of the fastest tells of a beginner.
Use kein (with the same der/die/das-style endings as ein) whenever you're negating a noun that would otherwise take ein/eine or no article at all:
| Gender | kein-form | Example |
|---|---|---|
| masculine | kein | Ich habe keinen Bruder. (accusative: kein→keinen) |
| feminine | keine | Ich habe keine Schwester. |
| neuter | kein | Ich habe kein Auto. |
| plural | keine | Ich habe keine Geschwister. |
Same accusative masculine change as Lesson 7's ein→einen: kein→keinen for masculine direct objects.
Use nicht to negate verbs, adjectives, and nouns that already have der/die/das or a name:
Ich komme nicht. (negating the verb)
Das ist nicht teuer. (negating an adjective)
Das ist nicht der Bus. (negating a specific, definite noun)
| Noun would take ein/eine or nothing | use kein/keine |
| Everything else (verbs, adjectives, definite nouns) | use nicht |
Cross-checked against the Goethe-Institut A1 practice materials.