Learn Hardcore Polish: Nauczyciel mówi, że zdanie powinno być proste, ale nie nudne. - The teacher says that the sentence should be simple but not boring.

In Polish że is mandatory to introduce a subordinate (reported‐speech) clause. It corresponds to English that, but unlike English you cannot drop it. Without że the sentence would be ungrammatical.

Why is zdanie in the nominative case here?

Because in the subordinate clause “…że zdanie powinno być…”, zdanie is the subject of the verb phrase powinno być, so it stays in the nominative.

Why is powinno used instead of musi?

powinno (from powinien) expresses should/ought to, a recommendation or softer obligation. musi (from musieć) means must/have to, a stronger necessity.

Why does powinno appear in its neuter singular form here?

Because it agrees with the subject zdanie, which is a neuter singular noun. In constructions like powinno być + adjective, the modal form agrees in gender and number with that subject.

Why are the adjectives proste and nudne also in the neuter singular nominative?

Adjectives in Polish must match the gender, number, and case of the noun they modify. Since zdanie is neuter singular nominative, both proste and nudne take the same form.

What’s the difference between ale and a, and why use ale here?

Both can translate as and/but, but ale signals a stronger contrast (“simple but not boring”). a often means “and” or “whereas” with a milder or more neutral contrast.

Why are there commas before że and before ale?

– Comma before że marks the start of a subordinate clause.
– Comma before ale separates two coordinated parts showing contrast. In Polish punctuation, you always set off these clauses/phrases with commas.

Why is the verb być necessary in “powinno być proste”? Couldn’t we say “zdanie powinno proste”?

You need być as the copula (“to be”) to link the modal idea (should) with the adjective. Omitting być would leave the adjective unattached, whereas Polish requires powinno być + adjective to form “should be ….”.