Same noun, same case, same adjective, different ending – what are the rules behind this?

Question

This question also has an answer here (in German):
Warum „anderen“ anstatt „anderem“?

Adjective endings in German seem inconsistent, even if one is aware that adjective endings depend on case, gender and number.

For example:

Ein roter Apfel liegt auf dem Tisch.
Der rote Apfel liegt auf dem Tisch.
Der Apfel ist rot.

In all three sentences, the same adjective (rot) describes the same noun (Apfel), which has the same case (nominative). Still, the adjective has different endings.

How is this phenomenon called and what are the rules behind it?

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Answer 1

TL;DR: Adjectives have to be declined not only according to the noun’s gender, number, and case but also according to the type of article used. If a verb links the adjective to the subject, the adjective is not declined at all.

Definite and indefinite articles

Using the German language, we differentiate between definite articles (bestimmte Artikel) and indefinite articles (unbestimmte Artikel)

Definite articles include:

this, these, that, those (English),
dieser, diese, dieses, jener, jene, jenes (German)

Indefinite articles (for our purposes) include:

a, many, few (English)
ein, eine, keiner, keine (German)

I will presume the distinctions between these two groups and their respective usages are understood.

Case 1 (weak declension)

When we use a definite article with a noun that we want to describe with an adjective, the adjective has to be declined according to the gender, number, and case of the noun:

Der rote Apfel liegt auf dem Tisch. (nominative, masculine, singular)

Ich sehe den roten Apfel. (accusative, masculine, singular)

Ich sehe die rote Tomate. (accusative, feminine, singular)

Ich sehe die roten Tomaten. (accusative, plural)

Ich sehe das rote Haus. (accusative, neutral)

(There is no distinction between genders in plural.)

Case 2 (strong declension)

When there is no article in front of the noun that we want to describe with an adjective, the adjective has to be declined according to the gender, number, and case of the noun as well, but in some cases (marked bold) the declension differs from the weak declension. This form is usually used with plural words and words that rarely or never appear in the plural (Singulariatantum), such as Wein (vine):

Roter Käse liegt auf dem Tisch. (nominative, masculine, singular)

Ich sehe roten Wein. (accusative, masculine, singular)

Ich sehe rote Milch. (accusative, feminine, singular)

Ich sehe rote Tomaten. (accusative, plural)

Ich sehe rotes Gemüse. (accusative, neutral)

The strong declension is called such because endings differ most often between genders, cases, and numbers.

Case 3 (mixed declension)

When we use an indefinite article with a noun that we want to describe with an adjective, the adjective has to be declined in yet another way. However, the declension always corresponds to either the weak or the strong declension (hence “mixed”):

Ein roter Apfel liegt auf dem Tisch. (nominative, masculine, singular)

Ich sehe einen roten Apfel. (accusative, masculine, singular)

Ich sehe eine rote Tomate. (accusative, feminine, singular)

Ich sehe keine roten Tomaten. (accusative, plural)

Ich sehe ein rotes Haus. (accusative, neutral)

Case 4 (predicative)

When we use a verb to link the noun to the adjective, we exclusively use the adjective’s base. No declension is needed:

Der Apfel ist rot.

Der Apfel schmeckt gut.

Er malte das Haus rot an.

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More information and word tables can be found here in German or here in English.

Answer 2

In 1 der rote Apfel the gender of Apfel is expressed by der. After der/die/das the adjective does not need a gender marker and the ending is only -e.

In 2 ein Apfel you can’t see the gender because ein has dropped the endings -er/-es. That is why the gender marker -er goes to the adjective and we say ein roter Apfel.

In 3 you have rot as a predicative adjective. In this position the adjective never has an ending.

In German there are article words with the gender endings -er/-es such as der, dieser, jener, welcher etc. After these article words the adjective has no gender endings, but only the endings -e/-en. This declension is called weak declension.

The second group of article words has dropped the gender markers -er/-es such as ein, mein, dein etc. Now the adjective takes on the task to mark the gender (strong adjective declension).

Answer 3

An alternative answer that does away with "mixed declension" and reference to definite or indefinite articles. This answer deals with attributive adjectives, i.e. those modifying a noun, since predicative and adverbial adjectives bear no endings.

Das hast du aber schön gesagt. (adverbial adjective)
Wir finden den Vorschlag nicht gut. (predicative adjective)

Basic Rules

Adjectives have two sets of endings: strong and weak.

1. The adjective bears a strong ending when it is not preceded by a determiner, or when the determiner preceding it bears no ending. Note hat prenominal genitives behave like a determiner without an ending.

Ø kühles Bier, ein-Ø kühles Bier
Ø schöne Blumen, welch-Ø schöne Blumen
mit Ø neuem Design, mit manch-Ø neuem Service
Merkels Ø jüngster Vorschlag

2. The adjective bears a weak ending when it is preceded by a determiner bearing an ending.

dieses kühle Bier
welche schönen Blumen
mit manchem neuen Service
der jüngste Vorschlag Merkels

3. The strong endings of adjectives are identical to the endings of determiners (pronominale Flexion: dies-er, jen-es, jed-e, welch-e, ...), with the exception of the genitive singular masculine and neuter, where the adjective has -en instead of -es.

jener Vorschlag = guter Vorschlag
welches Brot = frisches Brot

aufgrund dieses Problems ≠ aufgrund defekten Materials

4. The weak ending is -e in the nominative singular only and -en otherwise. (Note that, outside of the masculine singular, nominative and accusative are always identical, so that the accusative singular neuter and feminine also has -e).

dieser/dieses/diese kluge Mann/Kind/Frau

diesen klugen Mann
diese klugen Menschen
mit diesem/diesem/dieser/diesen klugen Mann/Kind/Frau/Menschen

5. Multiple adjectives modifying the same noun bear the same ending.

das umfangreiche technische Equipment
umfangreiches technisches Equipment

but: eine gut gewählte Analogie (gut modifies gewählte, not Analogie)

Note that rules 1 and 2 reference inflected word forms and not words (lexemes). In German, certain determiners (such as the the indefinite article ein, the negative determiner kein and the possessive determiners mein, dein, ...) have no ending in the nominative singular masculine and neuter. When they have no ending, they fall under rule 1 (ein kühles Bier); when they have one, they fall under rule 2 (mit einem kühlen Bier).

Adjective or Determiner?

Beware of homonyms such as the following.

mit einem einzigen Punkt (indefinite article)
mit dem einen Punkt (numeral adjective)

beide neuen Modelle (determiner, triggers weak inflection)
die beiden neuen Modelle (adjective, bears weak inflection)

Note that viel-, ander- are adjectives.

viele kluge Vorschläge, ein anderer Betroffener (strong by rule 1)
die vielen klugen Vorschläge, der andere Betroffene (weak by rule 2)

Deviations from Basic Rules

In the dative singular masculine and neuter, -m is often replaced by -n on adjectives following an adjective ending in -m, counter to rule 5.

mit umfangreichem technischen Equipment

A violation of the basic rules regularly occurs in appositions with wir.

wir Deutschen, wir beiden (weak, unexpected)
wir Deutsche, wir beide (strong, as expected)

The words folgend- and sämtlich- sometimes show unexpected strong inflection.

folgendes gesellschaftliche Problem (determiner triggering weak inflection)
das folgende gesellschaftliche Problem (adjective)
folgendes großes Problem (unexpected strong inflection; expected große)

sämtliche anwesende Bürger (unexpected strong inflection; expected anwesenden)

In certain fixed expressions or old-fashioned speech, endings may be dropped.

auf gut Glück
Ein garstig Lied! Pfui! ein politisch Lied! Ein leidig Lied! (Goethe)

Declension Table

	masc.	neut.	fem.	pl.
n.	-er -e	-es -e	-e -e	-e -en
a.	-en -en	-es -e	-e -e	-e -en
d.	-em -en	-em -en	-er -en	-en -en
g.	-en -en	-en -en	-er -en	-er -en

• Left forms are strong, right forms are weak.

• Observe how the strong forms are identical to those of determiners such as dies-er, with the exception of the genitive singular masculine and neuter.

• Observe how the weak forms have -e in the nominative singular (and accusative singular neuter and feminine) and -en elsewhere.

Terminology

• The term determiner is used instead of article to emphasize that these rules not only apply to definite and indefinite articles (der, ein, ...), but also words such as alle, jeder, welchen, keinem, ihres, ...

• The terms strong and weak have been used as far back as Jacob Grimm's Deutsche Grammatik (1822) (source).

Answer 4

1. Ein roter Apfel liegt auf dem Tisch.
2. Der rote Apfel liegt auf dem Tisch.
3. Der Apfel ist rot.

Das letzte Beispiel „Der Apfel ist rot“ gehört nicht zu den ersten beiden Beispielen. Es ist eine Farbenangabe eines Artikels (Prädikat), nicht ein Eigenschaftswort (Attribut) des Apfels.

In den beiden ersten Fällen, Apfel ist maskulin „ein roter Apfel“ das ‚r‘ beschreibt einen maskulinen Artikel. In „Der rote Apfel liegt auf dem Tisch“ ist das ‚r‘ bereits im Artikel vorhanden und ist dann im Eigenschaftswort nicht mehr nötig.