Learn Italian: Se il regista avesse cambiato la conclusione, non avrebbe vinto il premio. - If the director had changed the conclusion, he wouldn't have won the prize.

This sentence uses the third conditional to talk about an impossible or unreal past—something that didn't actually happen. The "if" clause uses se followed by the pluperfect subjunctive (avesse cambiato - had changed), and the result clause uses the past conditional (avrebbe vinto - would have won).

Why is the masculine article il used with regista, which ends in "-a"?

Many nouns ending in -ista that refer to professions or roles can be either masculine or feminine in the singular, depending on the person. Since it's il regista, we know this specific director is male. If it were a female director, it would be la regista. Note that their plural forms do change endings: i registi (masculine) and le registe (feminine).

Why do both parts of this conditional sentence use avere as the helping verb?

Both cambiare (to change) and vincere (to win) take direct objects here (la conclusione and il premio), making them transitive verbs. Transitive verbs always use avere as their auxiliary in compound tenses like the pluperfect subjunctive and past conditional. If the verbs involved motion or state of being, they would use essere.

There is no subject pronoun before non avrebbe vinto. How do we know it refers to the director?