Learn Hardcore German: Ich weiß nicht, wann ich staubsaugen soll, weil mein Terminplan voll ist. - I do not know when I should vacuum, because my schedule is full.

Because German places the conjugated verb at the end of subordinate clauses. Here wann ich staubsaugen soll is a subordinate clause (an indirect question introduced by wann), so soll goes to the very end.

What is the difference between wann and wenn?

wann is used for questions (direct or indirect) about time (“when”); wenn is used for conditional statements (“if”) or for repeated events (“whenever”). In this sentence we have an indirect question, so we use wann.

Why is there no zu before staubsaugen?

Because sollen is a modal verb. In German, modal verbs (like müssen, wollen, können, sollen) are followed directly by the infinitive without zu.

Why is staubsaugen written as one word and in lowercase?

German verbs are always lowercase, and many verbs are formed as compounds. staubsaugen is a single lexical verb made up of the noun Staub and the verb saugen. It’s not a separable-prefix verb, so it stays one word.

Why is Terminplan one word and masculine?

Terminplan is a compound noun combining Termin (appointment) + Plan (plan/schedule). German compounds are written as one word, and the gender is determined by the last component (Plan), which is masculine (der Plan → der Terminplan).

Why is voll not inflected in mein Terminplan ist voll?

Here voll is used predicatively (after the linking verb sein). Predicative adjectives in German remain uninflected. If voll were attributive (directly before a noun), it would carry an ending (e.g. mein voller Terminplan).

Why are there commas before wann and weil?

Both wann and weil introduce subordinate clauses. German grammar requires a comma to mark the start of each subordinate clause, so you get one comma before wann and another before weil.

Why is soll used instead of muss, and can I use muss here?

sollen expresses a softer obligation or recommendation (“should”), while müssen implies a necessity or compulsion (“must”). You could say Ich weiß nicht, wann ich staubsaugen muss, but that changes the nuance to “I don’t know when I have to vacuum” rather than “when I should vacuum.”

Why is nicht placed after weiß instead of at the end of the sentence?

In German main clauses, nicht generally follows the conjugated verb to negate the entire clause. Here it negates weiß (“I don’t know …”), so it appears immediately after weiß and before the subordinate clause begins.