Breakdown of Es ist der Detektiv, der die Lüge aufdeckt.
sein
to be
es
it
der
who, which, that (relative pronoun; die, das)
der Detektiv
the detective
Questions & Answers about Es ist der Detektiv, der die Lüge aufdeckt.
Why use the structure Es ist ..., der ... instead of just saying Der Detektiv deckt die Lüge auf?
This is a cleft sentence (Spaltsatz). By splitting a simple sentence into two parts using a dummy es, you place heavy emphasis on der Detektiv. It highlights that it is the detective—and absolutely nobody else—who uncovers the lie.
Why is der Detektiv in the nominative case here? Doesn't the Es act as the subject?
The verb sein (ist) connects two nominative phrases almost like an equals sign. The dummy subject Es is in the nominative, so the noun following it (der Detektiv) must also be in the nominative (acting as a predicate noun). It is never accusative.
Could we use wer instead of der to mean 'who uncovers the lie'?
No, because the relative pronoun here refers back to a specific, previously mentioned noun (der Detektiv). You must use the regular relative pronoun der (masculine, nominative). The word wer is only used when the person is unknown or generalized, like in 'Whoever uncovers the lie...' (Wer die Lüge aufdeckt...).
Why does the separable verb aufdeckt stay written as a single word at the end of the sentence?