• Yes/No questions:
  [[ The inflected verb is put at the beginning of the sentence ]] or
  [[ Inflected modal verb + subject + other parts (e.g., object) + verb ]]
  Kommst du? (Are you coming?)
  Habe ich geschlafen? (Did I sleep?)
  Können Sie Englisch Sprechen? (Do you speak English?)
  Darf ich das Fenster aufmachen? (May I open the window?)
• Asking for subject or object:
  [[ Interrogative pronoun + inflected verb + the rest ]]
  Welchen Ring hast du deiner Frau gekauft? (Which ring did you buy your wife?)
  Without knowing the gender and number of the noun, one can replace these pronouns by short forms:
  Was hast du deiner Frau gekauft? (What did you buy your wife?)
  Was machst du jetzt? (What are you doing now?)
  Wer geht ins Kino? (Who is going to the cinema?)

  SHORT FORMS	Person	Thing
  Nominative	wer	was
  Genitive	wessen	wessen
  Dative	wem	wem
  Accusative	wen	was

• Asking for a predicative:
  [[ Interrogative pronoun "Was" for nominal phrase, and "Wie" for else ]]
  Was ist ein Schmetterling? (What is a butterfly?)
  If asking for an adverb of a predicative, use "Wie":
  Wie hoch ist der Baum? (How tall is the tree?)
• Asking for a possessor:
  [[ Possessive interrogative article ("wessen" for all cases, genders and numbers) + inverted statement (inflected verb + the rest) ]]
  Wessen Auto hast du gesehen? (Whose car did you see?)
  Wessen hast du gesehen? (Whose did you see?) (Note: Wessen is now a pronoun)
• Asking for an adverb:
  [[ Interrogative pronoun (Wie) + conjugated verb + subject + rest of the sentence ]]
  Wie fliegt der Vogel am Himmel? (How does the bird fly in the sky?)
  Wie schnell fliegt der Vogel? (How fast does the bird fly?)
• Asking for position or adverbial clause:
  [[ Interrogative pronoun / "(preposition) + nominal phrase with the interrogative article" + conjugated verb + subject + rest of the sentence ]]
  Auf welchem Baum sah er den Vogel? (In which tree did he see the bird?)
  In welchem Jahr wurde dein Hund geboren? (In which year was your dog born?)
  Without knowing the gender and number of the noun, or even the kind of preposition, one almost always uses the short form, for example,
  Wo sah er den Vogel? (Where did he see the bird?)
  Wann wurde dein Hund geboren? (When was your dog born?)
  (Some Interrogative pronouns: Wo (where), Woher (from where), Wohin, Wann (when), Wieso (how come?), Weshalb (why), Warum (why), Weswegen (=weshalb))

1. Masculine Nouns:
   • Male person/animal: der Mann (man), der Sohn (son), der Arbeiter (worker)
   • Natural phenomena (rain, wind, snow, frost, etc.), season, month, and week name: der Regen (rain), der Schnee (snow), der Fruehling (spring), der Sommer (summer), der Herbst (autumn), der Winter (winter), der Januar (January), der Montag (Monday)
   • Direction words: der Osten (east), der Westen (west), der Norden (north)
   • Names of rocks: der Stein (stone), der Diamant (diamond)
   • Most derived-from-verb nouns and without any suffix: der Kauf (purchase), der Gang (walking; passage)
   • Most nouns with suffixes -er, -el, -ling, -s, -ich, and -ig: der Lehrer (teacher), der Schlüssel (key), der Schnaps (liquor)
   • Most nouns ended with -en (except those ending with -chen and infinitives used as nouns, such as: das Brötchen (roll, bun)): der Boden (earth), der Wagen (car)
   • Most nouns with loanword suffixes -ant, -ar, -at, -al, -ent, -eur, -ier, -or, -ist, -ismus, and -us: der Laborant (laboratory assistant), der Student (student), der Soldat (soldier), der General (general), der Doktor (doctor), der Sozialismus (socialism)
2. Feminine Nouns:
   • Female person/animal: die Frau (wife), die Kuh (cow)
   • Most names of flowers, trees and fruits: die Rose (rose), die Eiche (oak)
   • Number: die Eins (one), die Zwei (two), die Drei (three), die Neun (nine)
   • Nouns with the suffix of -in: die Arbeiterin (workwoman), die Studentin (female student)
   • Many nouns that end with -e: die Tasse (cup), die Frage (question)
   • Nouns with suffixes -ei, -heit, -keit, -schaft, -t(d), -ung: die Gesundheit (healthiness), die Gesellschaft (association,company), die Zeitung (paper)
   • All nouns with loanword suffixes -age, -enz, -esse, -euse, -ie, -ik, -ion, -itis, -taet, -ur: die Existenz (existence, living; life), die Politik (politics)
3. Neuter Nouns:
   • Young people and animals, and general animal names (both male and female): das Kind (child), das Kalb (calf), das Pferd (horse), das Rind (beef)
   • Names of cities, continents and most countries: das China (China), das Deutschland (Germany), das Paris (Paris)
   • Almost all names of metals and chemical elements: das Eisen (iron), das Gold (gold), das Jod (iodine)
   • All infinitives used as nouns: das Leben (life), das Denken (thought)
   • All other nominalized words: das Ich (self)，das Blau (blue)
   • Nouns with suffixes -chen , -lein , -sal , -sel or with prefix ge-: das Vöglein (bird), das Schicksal (fate)
   • Nouns with loanword suffixes -ett, -ment, -um: das Dokument (document), das Datum (date)
   • Collective nouns without suffixes -schaft, -ei: das Volk (people), das Besteck (cutlery, silverware)

General rules of Declension

Irregular declensions

Grammatical functions of German cases: