Basic adjective endings after ein-words (ein alter Mann)

Ein-words — ein/eine/ein, its negative kein, and the possessives mein, dein, sein, ihr, unser, euer — behave almost exactly like der-words when it comes to adjective endings. The only twist: in three spots, an ein-word doesn't show the noun's gender on its own, so the adjective has to step in and show it instead.

Quick shortcut: use the same endings you'd use after a der-word. The only difference is in three "genderless" slots — masculine nominative takes -er, and neuter nominative/accusative take -es — because ein alone doesn't reveal the gender there.

Why ein-words need extra help

A der-word like der or die always signals gender and case by its own ending. An ein-word doesn't: ein Mann, ein Auto — both use the bare form ein, with nothing to tell them apart. Compare that to der Mann vs. das Auto, where the der-word alone already distinguishes masculine from neuter.

Because ein can't do that job in those two forms (and eine is unambiguous only for feminine), German has the adjective pick up the missing signal. In the three places where the ein-word is ambiguous or bare, the adjective takes the ending a der-word would have had — -er for masculine, -es for neuter. Everywhere else, the adjective follows the same -e/-en pattern as after der-words.

The pattern, case by case

Only three cells differ from the der-word pattern: masculine nominative (-er), neuter nominative (-es), and neuter accusative (-es). Every other cell is -en, and feminine nominative/accusative is -e, exactly as it was after der/die/das.

• Ein alter Mann schläft. (An old man is sleeping.) — masculine nominative → -er
• Ich sehe einen alten Mann. (I see an old man.) — masculine accusative → -en
• Das ist ein neues Auto. (That's a new car.) — neuter nominative → -es
• Ich kaufe ein neues Auto. (I'm buying a new car.) — neuter accusative → -es
• Wir helfen einer alten Frau. (We're helping an old woman.) — feminine dative → -en

Possessives and kein follow the same rule

Mein, dein, sein, ihr, unser, euer, and kein all decline exactly like ein — including having a plural form (which ein itself lacks, since "a" has no plural). In the plural, there's no gender left to signal at all, so the pattern simplifies to the same -en ending used after der-word plurals:

• Mein neuer Kollege heißt Tom. (My new colleague is called Tom.) — masculine nominative → -er
• Keine neuen Schüler sind da. (No new students are here.) — plural nominative → -en
• Ich mag deine neue Wohnung. (I like your new apartment.) — feminine accusative → -e

Common mistakes

• ❌ ein alt Mann → ✅ ein alter Mann (masculine nominative needs -er, not a bare adjective — the ein-word gives no gender clue here)
• ❌ ein neue Auto → ✅ ein neues Auto (neuter nominative/accusative needs -es, easy to confuse with the feminine -e)
• ❌ Ich sehe einen alte Mann. → ✅ Ich sehe einen alten Mann. (accusative masculine still takes -en, same as after der-words)
• ❌ mit meinem alte Auto → ✅ mit meinem alten Auto (dative is always -en, regardless of gender, just like after der-words)

Quick check

Fill in the correct ending: -er, -e, -es, or -en?

1. Das ist ein neu___ Computer. (nominative, masculine)
2. Wir haben ein neu___ Haus. (nominative, neuter)
3. Ich mag deine neu___ Kollegin. (accusative, feminine)
4. Er spricht mit seiner neu___ Chefin. (dative, feminine)

Key takeaways

• Ein-words (ein, kein, and the possessives mein/dein/sein/ihr/unser/euer) take the same adjective endings as der-words in almost every case.
• The exception: masculine nominative takes -er and neuter nominative/accusative take -es, because the ein-word itself doesn't show gender there.
• Feminine nominative/accusative stays -e, and every dative case plus the entire plural stays -en — identical to the der-word pattern.
• Kein and the possessives also have a plural form (unlike ein itself), and the plural adjective ending is always -en.