In German, is there any rule for using 'denn' and 'weil'?

"weil" is because, but can also be translated: "as" or: "since"

"denn" is also "because", but can also be tranlated: "for"

Fragolina: "I lost the bus"????

Ich geh "denn" mal??????

Oh boy!

They have the same meaning, but they are not simply interchangeable!

Sometimes it's not possible to use "denn".

You can't use "denn" at the beginning of a sentence!

- "Weil ich spät dran war, habe ich den Bus verpasst."

= Because I was late, I lost the bus.

But if you put the first part as second, it's possible to use both, "weil" or "denn":

- "Ich habe den Bus verpasst, weil ich spät dran war." (verb at the end of the sentence)

= I lost the bus because I was late.

... but the word order changes if you use "denn":

- "Ich habe den Bus verpasst, denn ich war spät dran".

And furthermore, it doesn't express exactly the same in my opinion ... "weil" in the above and many other examples sounds like a natural explanation, while "denn" seems more like an additional information.

You should also know that Germans often use the wrong word order when they talk, so they use "weil" as if it was "denn". That happens because they add something spontaneousely.

"Ich kann nicht, weil ... Ich hatte einen Unfall." = I can't, because I had an accident.

Correct would be:

"Ich kann nicht, weil ich einen Unfall hatte."

In the spoken languages and some dialects "denn" is also used as the standard German "dann" (then).

- "Ich geh denn mal." = I'll go, then. (difficult to translate)

That's a site (in German) where you'll find a long explanation:

http://www.deutschesprache-schweresprache.de/dennw...

Denn Word Order

denn and weil have the same meaning.

....denn sie wissen nicht, was sie tun. = Because they don't know what they're doing. [they know not what they do]

....weil sie nicht wissen, was sie tun. = Because they don't know what they're doing.