Some time ago I answered this question on Quora about German Grammar. As I have my own homepage now, here it is as well!:
What is the difference between German words, when both of are (you) English „dich“ and „dir“?
That is a short (and very logical) question that requires a bit of a lengthy answer.
German grammar works a bit different than English grammar. (Most people will say it is more complicated. I agree.)
Introduction to Cases
In German we have “cases”. Every noun and pronoun has one of four cases according to the function it has in any given sentence. The case is sometimes shown in changing endings of the words, very often you only see it in the article going with the word.
English Word Order versus Cases in German
English does not have cases like German, but handles that by order of words in a sentence.
English “The man sees the dog” would be German “Der Mann sieht den Hund”. Now if you want to say it the other way around in English it would be “The dog sees the man”. The only difference is the sequence of the words. In German I could say “Der Hund sieht den Mann”, or “Den Mann sieht der Hund”. So because we have case we have bigger flexibility in what sequence we put words in sentences.
That is the basic idea of cases.
Finally: „Dich“ and „Dir“ (which are both „You“)
“Dich” und “Dir” are different cases. “Dich” is the “4th case” or “Akkusativ” and “Dir” is “3rd case” or “Dativ”.
If you have a transitive verb (a verb like “I see the dog” – the action of the verb goes directly over to someone or something. I love my husband. He hates cleaning. She reads a book. These are all transitive verbs. Works the same in German) in German you have to use the “4th case”. And the 4th case for “you” (German “du”) ist “dich”. So “I see you” is “Ich sehe dich.” “She likes you” is “Sie mag dich”.
The “3rd case” is used for example when you have a word like “give” or “teach” which needs another information to finish the sentence. “I give you the book” German: “Ich gebe dir das Buch”. “Das Buch” is 4th case (it is the thing given) and “dir” is 3rd case. Same with “I will teach you English” “Ich werde dir Englisch beibringen.” “Englisch” is “4th case” and “dir” “3rd case” as said before.
Isn’t there an easier way to understand this?
The easier way to understand and learn it however is that a verb or preposition can ask for a specific case and when you learn a word you learn that as well and use it in example sentences until you have it.
I am not sure what your level of German was. Either you are happy now and have the explanation you need – in that case: I am glad that I could help.
German is made way to complicated
If however you find this a bit confusing, don’t be discouraged. I would never teach that in that speed and would make sure that every step of this is fully understood before going to the next.
In general my experience says that there is a tendency of giving to much emphasis to grammar to early in the student’s progress. That makes things unnecessarily hard.