Learn Hardcore German: Der Abstieg vom Berg ist heute schwierig, weil der Weg nass ist. - The descent from the mountain is difficult today because the path is wet.

All German nouns are always written with an initial capital letter, regardless of their position in the sentence. Since Abstieg is a noun, it must be capitalized.

What does Abstieg mean exactly, and what is its gender?

Abstieg means “descent” (the act of going down), here specifically down a mountain. It is a masculine noun, so its nominative article is der Abstieg.

Why is vom used here instead of von dem?

vom is simply the contracted form of von dem. In everyday German, von dem often contracts to vom for smoother pronunciation and writing.

What case is vom Berg, and why?

The preposition von always requires the dative case. Therefore, von dem Berg becomes vom Berg, with dem Berg in the dative.

What is the function of vom Berg in this sentence?

It’s a prepositional phrase indicating origin or starting point: the descent starts from the mountain. Grammatically, it acts as an adverbial modifier of place.

Why is heute placed between ist and schwierig?

heute is a temporal adverb (indicating time). In German main clauses adverbs typically go in the “mid-field” (between the finite verb and other sentence elements). The usual order is Verb – Adverb of Time – (other elements), so ist heute schwierig is natural.

Why doesn’t schwierig have an ending, like schwierige or schwierigen?

Here schwierig is a predicative adjective (it comes after the copula ist). Predicative adjectives in German are not inflected, so they appear in their base form.

Why is the verb ist at the end of the clause weil der Weg nass ist?

weil is a subordinating conjunction, and in German subordinate clauses the finite verb moves to the final position. Hence you get weil der Weg nass ist.

Why is there a comma before weil?

German punctuation rules require a comma before any subordinate clause. Since weil introduces a subordinate clause, you must place a comma right before it.

Can I replace der Weg with er in the subordinate clause?

Yes. Once you have introduced der Weg (masculine), you can use the pronoun er in the subordinate clause: “… weil er nass ist.”

What’s the difference between weil and denn in this context?

Both mean “because,” but weil is a subordinating conjunction (the verb goes to the end of its clause), whereas denn is a coordinating conjunction (normal word order stays).
Example with denn:
Der Abstieg ist schwierig, denn der Weg ist nass.
Here the verb ist remains in second position after denn.