"Nein, es ist jemand anderes" – Declension of "andere"

Question

• Nein, es ist jemand anderes.
• Das ist etwas anderes

Could someone please explain why is anderes and not andere?

Since I believe anderes is here a predicative adjective it should go in the base form: andere

Answer 1

What is anderes?

Anderes is a (probably substantivated) adjective (indefinite base forms: anderer/andere/anderes). It is an apposition to the indefinite pronouns jemand and etwas, respectively:

• Nein, es ist [jemand [anderes]]
• Das ist [etwas [anderes]]

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Which form is anderes here?

This is not so unambiguous. The Duden-Grammatik (§ 1586) identifies it as perceived as nominative 'or' accusative neuter, but also states that it was a genitive form originally.

Maybe the reason for your confusion is that there are two nominative neuter singular forms of anderes: the 'weak' (as das andere Haus, das Andere) and the 'strong' (ein anderes Haus, ein Anderes). Since jemand and etwas are indefinite, we need to use the 'strong' form anderes here.

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Which case of anderes is required?

You expected an endingless form because you assumed it was a predicative adjective. But as we saw, it is an apposition instead. As 'close' apposition, the case of anderes needs to be congruent with the syntactical function of jemand or etwas, respectively, even if they themselves remain without ending.

In your examples, the whole phrase indefinite pronoun + apposition is a predicative nominative as required by the verb sein. Thus, anderes is nominative.

In other contextes, we might need the accusative (which has the same ending) or the genitive or dative (which have separate endings):

Ich habe jemand anderes gesehen. (accusative, same ending as nominative)

Ich bin jemand anderem begegnet. (dative)

Ich wohne in jemand anderen Haus. (genitive, somewhat unusual)

Sometimes forms of jemand with endings are used:

Ich wohne in jemandes anderen Haus.

Same is possible with the pronouns niemand or wer:

Das ist niemand anderes.

Das ist wer anderes.

To avoid this hassle, you could use the invariable adverb anders with jemand, niemand and wer (but not with etwas):

Nein, es ist jemand anders.

Ich spreche mit jemand anders.

Answer 2

Grammatically, ander‑ stands in apposition to the pronoun jemand. Some similar constructions:

Hast du jemand Interessanten getroffen?

Das sagt niemand Geringeres als die Kanzlerin selbst.

Ich hab gestern wen Nettes kennengelernt.

Historically speaking, ander- is an adjective (the ‑er‑ is in fact the comparative ending). A (nominalised) adjective in apposition to a masculine pronoun such as jemand should show the strong masculine singular ending, e.g. -er in the nominative and -em in the dative:

oder daß einer ein Kleinod mit einem Bildnis finde, welches vermutlich jemand anderer vorher verloren hat (1)

und erzählte ihr alles, mehr als sie je irgend jemand anderem erzählt hatte (2)

However, there are also forms invariably ending in -es, similar to niemand Geringeres and wen Nettes above. For instance, in the accusative and dative:

der Mensch sieht in jedem Übelbefinden und Mißgeschick etwas, wofür er irgend jemand anderes leiden lassen muß (3)

wir können uns selber kitzeln und dabei genau dieselben Empfindungen haben, als wenn wir von jemand anderes gekitzelt würden (4)

I think that § 1586 of the Duden grammar (as cited by amadeusamadeus) is correct in that the forms in ‑es are former genitives. However, examples such as (4) are incompatible with the theory that ‑es has been reinterpreted as a neuter singular ending, as neuter dative singular would be ‑em.

As far as the distribution of unexpected invariable ‑es vs. the expected masculine ending ‑er, ‑en, ‑em is concerned: In the dative, masculine ‑em is more popular than invariable ‑es. In the nominative, the reverse is true: invariable ‑es is more popular than masculine ‑er.

A minor complication for ander‑ is that the inflected adjective anderes can be shortened to both andres and anders; in the latter variant, it is identical to the adverb anders (which is itself derived from the genitive anderes, with syncope of the second ‑e‑).