La fonte di cui parlo è sicuramente affidabile.
The source I am talking about is definitely reliable.
Breakdown of La fonte di cui parlo è sicuramente affidabile.
essere
to be
di
of, from
parlare
to speak / to talk
sicuramente
surely / certainly
Questions & Answers about La fonte di cui parlo è sicuramente affidabile.
Why do we use di cui here instead of just che?
Because the verb is parlare di (to talk about). When a relative pronoun follows a preposition like di, you must use cui instead of che. Literally, this sentence says 'The source of which I speak'.
Why does the preposition di go before cui?
In Italian, you can never leave a preposition at the end of a phrase like we often do in everyday English ('the source I am talking about'). The preposition must always go right before the relative pronoun, just like in formal English: 'the source about which I am talking'.
How does the word sicuramente (definitely) get its ending?
Why doesn't the adjective affidabile end in -a to match the feminine noun la fonte?
Because adjectives that end in -e in the dictionary, like affidabile (reliable), don't change for gender. They use the same -e ending for both masculine and feminine singular nouns. If we were talking about multiple sources, it would change to the plural form affidabili.