Adjective endings — gently
When a German adjective sits AFTER the noun (predicative — Der Apfel ist grün.), it takes no ending. Easy. But when it sits BEFORE the noun (attributive — 'the green apple'), it must take an ending. The endings depend on (1) the case, (2) the gender/number of the noun, and (3) what kind of article comes before. We'll cover the two friendliest situations: with a definite article (der/die/das — "weak" endings) and with an indefinite article (ein/eine — "mixed" endings). The bare-noun case comes later.
After the definite article — weak endings (just -e or -en)
When der, die, das, die (pl.) — or any dieser, jeder — is doing the heavy lifting of marking the case, the adjective only has to add a quiet -e or -en. Two endings, that's all. Nominative singular: der grüne Apfel, die grüne Lampe, das grüne Buch. Accusative singular feminine and neuter: die grüne Lampe, das grüne Buch. Everywhere else — accusative masculine, all dative, all genitive, all plural — it's -en: den grünen Apfel (acc. m.), dem grünen Apfel (dat. m.), die grünen Äpfel (plural).
The 5-cell weak pattern (memorize this)
For nominative and accusative — the cases you'll meet first — the pattern is: nom. m. -e, nom. f. -e, nom. n. -e, nom. pl. -en, acc. m. -en, acc. f. -e, acc. n. -e, acc. pl. -en. So only the masculine accusative breaks the -e pattern in the singular. Ich sehe den grünen Apfel. = I see the green apple. Ich sehe die grüne Lampe. = I see the green lamp. Ich sehe das grüne Buch. = I see the green book. Ich sehe die grünen Äpfel. = I see the green apples.
After the indefinite article — mixed endings
ein by itself is ambiguous: it doesn't show whether the noun is masculine (ein Apfel) or neuter (ein Buch) — same form. So in those three slots — masculine nominative, neuter nominative, neuter accusative — the adjective has to step up and carry the case marker that the article didn't. It does that with -er (m.) and -es (n.). Everywhere else the indefinite article looks fine, so the adjective relaxes back to weak -e / -en. ein grüner Apfel (m. nom.) — adjective shows masculine. eine grüne Lampe (f. nom.) — back to -e. ein grünes Buch (n. nom., n. acc.) — adjective shows neuter.
The 5-cell mixed pattern (memorize this)
Nom. m. -er, nom. f. -e, nom. n. -es, acc. m. -en, acc. f. -e, acc. n. -es. The dative endings are all -en (einem grünen Apfel — to a green apple). The masculine accusative is -en in BOTH the weak and mixed patterns — that's a nice freebie. Compare: der grüne Apfel vs ein grüner Apfel (only the m.-nom. ending differs); das grüne Buch vs ein grünes Buch (only the n.-nom./acc. ending differs). The possessives mein, dein, sein, ihr etc. and the negative kein all behave like ein — same mixed pattern.
How to actually do this in your head
Step 1: figure out the case (nominative for the subject, accusative for the direct object, dative after dative prepositions or as indirect object). Step 2: figure out the gender of the noun. Step 3: ask — does the article already show the case clearly? If yes (definite article) → adjective gets -e or -en (mostly -e in nom./acc. singular, -en everywhere else). If no (indefinite, in m. nom., n. nom., n. acc.) → adjective shows the case ending -er or -es. With practice, this becomes automatic. Don't stress about getting every form right at A1 — even native speakers fumble dative plurals occasionally.
