A section of A guide to German
Case and gender
In English, nouns are fairly simple. There are no gender distinctions, and they are not affected by grammatical case. Furthermore, to form the plural, you simply add an s (or -es if appropriate), with just a few exceptions, e.g. "child/children".
German nouns are more complicated. All nouns in German belong to one of three genders - masculine, feminine, or neuter. With nouns that refer to people, e.g. "father", there is a near-perfect correlation between sex and gender, so "man", "father" and "brother" are all masculine (der Mann, der Vater and der Bruder), while "woman", "mother" and "sister" are all feminine (die Frau, die Mutter and die Schwester). But the gender of other nouns cannot be predicted from their meaning and must be learned. (And there is of course the well-known example of Mädchen, which means "girl" but is neuter, although this is because any noun ending in the diminutive form -chen is neuter; so, for that matter, is any noun ending in -lein, including a word familiar to many non-Germans, Fräulein.)
The gender of a noun must be known if you are to qualify it with the correct definite and indefinite article (which in English is simply "the" and "a"/"an"). You must also take it into account when declining adjectives, that is, giving them the correct ending for the noun they are describing.
In addition, German nouns are affected by the property known as "case". A noun's case is the role it is playing in a sentence - for example, it may be doing a verb (subject) or having a verb done to it (object). In English we still use this for pronouns - any child knows to say "He is tall" but "I saw him", even if "he" and "him" is the same person; German uses this for pronouns like English does, but extends it to all nouns. To correctly use a German noun (and its qualifiers and adjectives), you must take into account its case: whether it is nominative, accusative, dative or genitive.
The nominative case is for the doer of a verb in a sentence (known as the subject), for example "the man" in the "the man sees the boy". It is also the default case for any noun referred to without context, for example in a dictionary entry.
The accusative case is for the direct object of a verb, the noun in a sentence which is having something done to it. In "the man sees the boy", "the boy" is the direct object - and is therefore accusative - because it is being seen by the man.
The dative case is for the indirect object of a verb, something upon which the verb is not done, but rather done "for" or "in mind of". In the sentence "I baked my sister a cake", "my sister" is the indirect object - she is not being baked, but rather the baking is being done for her; she is dative, whereas the cake, which is being baked, is accusative.
The genitive case is used to show possession. In "the best member of our club", or "our club's best member", "our club" is possessing the "member" and is genitive. The genitive construction is used in German to show possession when the genitive noun is not a person's name or a pronoun.
German has six definite articles (der, die, das, den, dem and des) and six indefinite articles (ein, eine, einen, einem, einer and eines). The sheer number is not necessarily as confusing as it may sound - Italian, for example, also has six definite articles, but they are not too hard to use correctly. Unfortunately in German their meanings have been mixed around like lottery balls, not following any logical system, and you must simply learn the combinations.
German plurals act the same regardless of the gender of the singular noun, so they can be treated as a fourth gender. Here, then, are all the possible combinations of gender and case:
Masculine Feminine Neuter Plural
Nominative der die das die
Accusative den die das die
Dative dem der dem den
Genitive des der des der
Thus all the forms except das can apply to more than one gender, which doesn't make things very easy; you just have to learn the table.
Here are some examples. Mann, for "man", and Hund, for "dog", are both masculine. "The dog bit the man" is der Hund biss den Mann. Der Mann biss den Hund means "the man bit the dog", but Den Mann biss der Hund means "the dog bit the man", because den Mann is the accusative form while der Hund is nominative. "The woman bakes the man a cake" is die Frau bäckt dem Mann einen Kuchen, while "the man bakes the woman a cake" is der Mann bäckt der Frau einen Kuchen.
The indefinite articles line up in a similar way:
Masculine Feminine Neuter
Nominative ein eine ein
Accusative einen eine ein
Dative einem einer einem
Genitive eines einer eines
Thus "a dog bit a man" is ein Hund biss einen Mann - or, if you like, einen Mann biss ein Hund. (This changing of word order is useful for emphasis and for things like narrative and poetry, and is covered in A guide to German : Word order.)
To use the genitive, the noun being possessed comes first, followed by its possessor (the genitive noun). If the possessor is masculine or neuter singular, it adds an -s or -es. Thus "the roof of a house" is das Dach eines Hauses, and "the names of the men" is die Namen der Männer.
Qualifiers thus inflect for all nouns. There is a class of nouns, known as the "weak nouns", which themselves inflect for case - that is, the word itself changes. (Although it sounds bizarre to the English speaker, this is actually a feature of many languages, and is found even in Esperanto.) These are all masculine, with one neuter exception (das Herz), and they add -n or -en in all cases except the nominative. Thus "he is a hero" is er ist ein Held, but "I know a hero" is ich kenne einen Helden. In the genitive, most weak nouns use this -n ending instead of the normal -s, but a few add both, so "the origin of the name" is der Ursprung des Namens, not des Namen.
Nouns are also thrown out of the nominative case when they are the object of a preposition (a word like "in", "through", or "under"). For example, "the book by the telephone" is das Buch neben dem Telefon, dem Telefon being dative. Prepositions take either the accusative, the dative, the accusative or dative, or the genitive, and are discussed in Gorgonzola's German prepositions.
In English, to make a plural you just add an -s. In German it's not so simple - there are in fact eight ways of doing it. Some nouns don't change at all, like "sheep" in English. Some add an umlaut to the stem vowel. Some add the suffix -e. Some add the suffix -e and an umlaut. Some add the suffix -er. Some add the suffix -er and an umlaut. Some add the suffix -n or -en. And some add the suffix -s, like in English.
Note furthermore that all plurals end in -n if they are dative; if they already end in -n they stay the same, otherwise an -n or -en is added. The exception is plurals which normally end in -s; these do not add -n.
To be 100% certain, you must just learn the plural of any noun, but there are some tendencies which you may find helpful to remember. Nouns ending in -en never add a suffix, although they may still add an umlaut. Virtually all nouns ending in -e add an -n. Most feminine nouns add -n or -en, although a number of common ones do not. All you can do is get a feel for it - but stay prepared for exceptions, as you always have to do with German.
750 German Verbs and Their Uses (1992) provides this table of examples of plurals; I have added the words' meanings.
singular plural meaning
das Zimmer die Zimmer ("rooms")
der Mantel die Mäntel ("coats")
der Garten die Gärten ("gardens")
der Tisch die Tische ("tables")
der Stuhl die Stühle ("chairs")
das Bild die Bilder ("pictures")
das Buch die Bücher ("books")
das Haus die Häuser ("houses")
die Uhr die Uhren ("watches")
die Lampe die Lampen ("lamps")
die Freundin die Freundinnen ("girlfriends")
das Radio die Radios ("radios")
According to Steven Pinker's Words and Rules, the -s ending has been called the Notpluralendung - "emergency plural ending" - and is used in a variety of situations where others would seem unusual: recently made-up words, obviously foreign imports (e.g. Radio), proper nouns, abbreviations, pluralised quotations, etc. It is not related to the English -s, but rather was incorporated into standard German in the nineteenth century through imports from Low German (spoken in the north), Dutch, English and French.