Off the back of Why is it "Tumoren" and not "Tumore"?, why is the Genitiv "des Tumors" and not "des Tumoren"?

Duden: der Tumor; Genitiv: des Tumors, Plural: die Tumoren, umgangssprachlich auch: Tumore

My understanding is that to form the Genitiv from the Nominativ der oder das it is typically Substantiv + s, i.e.

der Vater --> des Vaters
das Hotel --> des Hotels

albeit sometimes with an 'es'

das Jahr --> des Jahres

except when the Plural ending is 'en'

der Therapeut, die Therapeuten --> des Therapeuten

So since the plural of der Tumor is die Tumoren, why is the Genitiv "des Tumors" and not "des Tumoren"?

  • 1
    It's hard to answer your question. You say, that your rule of thumb only applies in the typical case. So, what if the answer to your question was just: "This is not a typical case". Of course, this would hardly satisfy you. But what kind of answer would that be, that satisfies you? Would you be satisfied by a bunch of counterexamples to your rule of thumb, for instance?
    – Jonathan Herrera
    Commented Apr 9, 2019 at 12:59

2 Answers 2


Maskuline Nomen mit n-Plural können zwei verschiedenen Deklinationsklassen angehören: der schwachen, die -(e)n im gesamten Singular mit Ausnahme des Nominativ haben, und der gemischten, die im Genitiv Singular die Endung -(e)s haben.

schwach: Experte, Herr, Junge, Kollege, Kunde, Name, Pilot, Soldat, …

gemischt: -tor, Schmerz, Staat, Strahl, …


There's another representative of the gemischte Deklination you're certainly familiar with: der Doktor; des Doktors // die Doktoren. And if you're willing to forget the additional -e- for a second: der Schmerz; des Schmerzes // die Schmerzen. A neuter one: das Elektron; des Elektrons // die Elektronen. Mind that none of these are an exception, but the rule.

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