Weil vs. Denn

While there is not difference in meaning between "weil" & "denn", they are not interchangable: You cannot simply take a sentence that uses "weil" and replace "weil" with "denn".

Weil & Denn Explained

Weil

The reason for this is that weil & denn "dock onto" different sentence structures. "Weil" requires a subordinate clause, whereas "denn" requires a main clause. Let's have a look at sentence using weil:

What comes after "weil" cannot stand on its own. It's a subordinate clause. "Ich Durst habe" is not be a correct sentence in German.

Denn

"Denn", however, works differently to "weil". It introduces a main clause. So the very same sentence with "denn" has a slightly different word order:

"Ich habe Durst" can stand on it's own: it's a main clause.

And this is the reason why you cannot just swap "weil" & "denn" out however you please.

Denn cannot stand at the beginning of a sentence

Another difference is that "denn" can never stand at the beginning of a sentence. You cannot introduce a sentence with "denn".

So you could say:

But you could not say:

Examples with weil & denn

Weil

Here are two more basic dialogues using "weil":

Warum warst du krank? Und wie lange?

Why were you sick? And for how long?

Ich war die ganze letzte Woche krank, weil ich mich auf Katjas Hochzeit nicht warm genug angezogen habe!

I was sick the entire last week because I didn't dress warmly enough at Katja's wedding!

Warum kommst du nicht mit auf das Konzert?

Why aren't you coming to the concert?

Weil ich leider kein Geld habe. Aber nächstes Mal komme ich mit!

Because I don't have any money. But next time, I'll come along!

Denn

And here are two example dialogues using "denn":

Ich freue mich auf das Konzert, denn ich war schon so lange nicht mehr aus!

I'm looking forward to the concert because I haven't been out for so long!

Ich freue mich auch! Wann gehen wir?

I'm excited too! When are we going?

Wieso seid ihr nicht pünktlich angekommen?

Why didn't you arrive on time?

Wir mussten auf der Autobahn sehr langsam fahren, denn es regnete zu stark!

We had to drive very slowly on the highway because it was raining heavily!