Strong, weak, and mixed adjective endings
L19 introduced adjective endings. Now we put the whole system on one page. Every German adjective in front of a noun gets an ending. Which ending depends on what comes BEFORE the adjective: (1) strong when there's no article (or just a quantity word like viel, etwas) — the adjective itself has to carry the case info; (2) weak after a definite article (der/die/das/diese) — the article already shows case, so the adjective just adds a placeholder -e or -en; (3) mixed after ein/kein/mein — partly strong (where ein has no ending) and partly weak (everywhere else).
Why three patterns?
German wants the case and gender visible somewhere in the noun phrase. If the article shows it (der Mann, dem Mann, den Mann), the adjective can relax → weak. If there's no article at all (kalter Wein), the adjective has to carry the load → strong endings that look like the article. ein is half a problem: ein Mann doesn't show masculine, eine Frau does — so the adjective uses strong endings exactly where ein has no ending of its own → mixed. One mental model: 'whichever element shows case must wear the ending; the other one wears the lazy -e/-en.'
Weak endings — after der-words
After der, die, das, diese, jene, jeder, welcher, alle: the adjective takes only -e or -en. The pattern: nominative singular and neuter/feminine accusative singular take -e; everything else takes -en. der alte Mann, die alte Frau, das alte Buch, die alten Bücher — those are all the -e spots. Every other case (acc. m., all dative, all genitive, all plural beyond nominative) → -en. Ich helfe dem alten Mann. Ich kenne die alten Männer.
Mixed endings — after ein-words
After ein, kein, mein, dein, sein, ihr, unser, euer, Ihr: same as weak EXCEPT three spots where ein itself has no ending. There the adjective borrows the strong ending. ein alter Mann (m. nom. — ein has no ending, adjective takes -er), ein altes Buch (n. nom./acc. — ein has no ending, adjective takes -es), and the m. accusative IS regular (einen alten Mann, ending on the article → adjective just -en). Everywhere else: -en.
Strong endings — no article at all
When there's no article (or only a quantity word like viel, etwas, mehr, wenig), the adjective itself takes the strong endings — the same forms the definite article would have shown. kalter Wein (m. nom. — like der, ending -er). kaltes Wasser (n. nom./acc. — like das, ending -es). kalte Milch (f. nom./acc. — like die, ending -e). kalten Wein (m. acc. — like den). mit kaltem Wasser (n. dat. — like dem). One twist: in masculine and neuter GENITIVE, the noun already carries the -s/-es ending, so the adjective takes weak -en: trotz kalten Wassers.
The three patterns side by side
der gute Tag (weak — -e), ein guter Tag (mixed — -er, because ein is empty), guter Tag! (strong — same -er). das alte Haus / ein altes Haus / altes Haus. die schöne Frau / eine schöne Frau / schöne Frau (no difference: feminine die and eine both show case, and bare-nominative feminine looks the same). After articles: weak -e or -en. After ein-words: borrow strong only at the three empty spots. No article: pure strong throughout (except m./n. genitive).
Plural — easier than it looks
Plural simplifies a lot. After die / diese / meine / keine / alle, every plural adjective ends in -en: die alten Bücher, meine guten Freunde, alle netten Leute. With NO article (pure strong plural), use the article-like endings: alte Bücher (nom./acc.), alten Büchern (dat. — note also the -n on the noun), alter Bücher (gen.). Pure-strong plural is mostly written and formal; in everyday speech you'll usually have die / meine / keine in front.
Quick recipe
Three questions in order: (1) Is there an article-like word? If NO → strong. (2) If YES, is it a der-word (article shows case)? → weak. (3) If YES but it's an ein-word → mixed (strong ending only where ein is empty: m. nom., n. nom./acc.). The default fallback ending is -en — when in doubt and it's not one of the -e/-er/-es/-em spots, -en is right surprisingly often.
