You've already learned about object clauses that serve as the object in an independent clause. In the same way, subject clauses are dependent clauses that function as the subject of the sentence. Like all dependent clauses, they need a main clause or another dependent clause to complete their meaning and cannot stand on their own. You can recognize a subject clause (and also an object clause) by the fact that the superordinate clause would be incomplete without it.

Examples:
Wer nicht hören will, muss fühlen.
Wer's glaubt, wird selig.

In each of the above sentences, the subject of the main clause is itself a dependent clause. Without it, the sentence would be incomplete and have no subject.

Subject clauses often begin with interrogative pronouns, such as "wer" and "was".

Just like single-word subjects, subject clauses answer the question "who?" or "what?".

Example:
Wer's glaubt, wird selig. – Wer oder was wird selig? – Wer's glaubt.

You can tell whether it's a subject clause if the entire clause can be replaced by a single word.

Example:
Wer's glaubt, wird selig.
Substitution test:
Wer oder was wird selig? – Der wird selig.

Subject clauses can also be introduced by the conjunctions "dass" and "ob".

Examples:
Ob er selig wird, ist unbekannt.
Dass der selig wird, ist sicher.