Difference between "den" and "ihn"?
In this little diaglog containing 3 sentences:

1) Der Schlu:ssel ist nicht da.
2) Suchst du ihn bitte.
3) Den habe ich schon gesucht.

Instead of "den" in sentence 3, could I use "ihn" another time? If so, is the meaning different?
And vice versa, instead of "ihn" in sentence 2, could I use "den"?

I have hard time seeing the difference between "den" and "ihn". I believe that "den" can be used when we already know what we are talking about and referring to it (like "le" in French, for example). But what about "ihn"?

Question

Difference between "den" and "ihn"?
In this little diaglog containing 3 sentences:

1) Der Schlu:ssel ist nicht da.
2) Suchst du ihn bitte.
3) Den habe ich schon gesucht.

Instead of "den" in sentence 3, could I use "ihn" another time?  If so, is the meaning different?
And vice versa, instead of "ihn" in sentence 2, could I use "den"?

I have hard time seeing the difference between "den" and "ihn".  I believe that "den" can be used when we already know what we are talking about and referring to it (like "le" in French, for example).  But what about "ihn"?

Answer

BTW, never write u: for ü. If your keyboard doesn't have umlauts, the official rule is ä = ae, ö = oe, ü = ue, and ß = ss.

In principle, "den" und "ihn" can both be used in both sentences. However, the way they are used in the example sentences is the natural way. "ihn" is the (neutral) pronoun (= it). "den" (slightly lengthened and emphasized when speaking) stresses that it's about this particular one (= this one, that one). It's short for "(genau) den Schlüssel/diesen Schlüssel".

It can work in a similar way in English:

1) The key is gone.
2) Could you please look for it?
3) But I already looked for that key.