A Question about Nominative, Genitive, Dative and Accusative in German.
For instance, "Ich danke meinem Lehrer für seine Erklärung".

1. Why "meinem" not "meinen"? I think "Lehrer" here is object, so the article should be "den" not "dem".
2. Is "seine" here the nominative or accusative? I'm a little confused.

Vielen danke!
Zhao Lei

Question

A Question about Nominative, Genitive, Dative and Accusative in German.
For instance, "Ich danke meinem Lehrer für seine Erklärung".

1. Why "meinem" not "meinen"? I think "Lehrer" here is object, so the article should be "den" not "dem".
2. Is "seine" here the nominative or accusative? I'm a little confused.

Vielen danke!
Zhao Lei

Answer

Hello Zhao. 
You're right in thinking that Lehrer is the object, but it's the object of "danken," whose object is always dative. there are maybe 25 or so verbs that always take a dative object. Some others are "helfen", "antworten," and "glauben."

Erklärung is accusative here, because it follows the preposition "für," which always takes accusative. Such prepositions are bis, durch, für, ohne, gegen, and um

Answer

Learn the verbs together with the cases. It's "jemandem (Dat) für etwas (Akk) danken". Good dictionaries, e.g. Pons (http://de.pons.com/) show you these patterns when you look up verbs.

Answer

Could you please help me to fulfill the following blanks?	
Sorry I can not ask any questions today, so I'm here to ask for help.

the first person	the second person	the third person	 honorific	
1 ich	 du es er sie Sie 
2	
3 mir dir	
4

the first person	the second person	the third person	 honorific	
1 wir	 ihr sie Sie 
2	
3	
4

Answer

preposition /ˌprɛpəˈzɪʃən/ 介詞