18.104.22.168 Prima che, if the subject of the main sentence is as well the subject oft the subordinate clause
We have already seen when discussing the conjunction dopo che that the subordinate clause introduced by this conjunction can be substituted with an infinitive if the infinitive shares the subject with the verb in the main sentence.
The subordinate clause has his own subject
Dopo che mi aveva detto questo, non volevo più vederlo.
After he had said me that, I didn' t want to see him anymore.
The subject of the subordinate clause and the subject of the main clause are the same
Dopo aver letto la sua lettera, ho capito meglio le sue intenzioni.
After having read his letter, I understood his intentions better.
It is usefull to see that dopo che is a conjunction, but the dopo followed by an infinitive is a preposition, the infinitive is a substantivated verb and instead of an substantivated verb we can use just any noun.
Dopo aver mangiato, fumo una sigaretta. or. Dopo pranzo, fumo una sigaretta.
After dinner I smoke a cigarette.
From that we can deduce that the possibility to substitute a subordinate clause with an infinitive is only possible if there exists a preposition which corresponds to the conjunction. The number of conjunctions of this type is limited. One of the conjunctions with a corresponding preposition is prima che.
conjunction (with congiuntivo)
Prima che ti risponda, devo informarmi.
prepositions (with an infinitive used as a noun)
Prima di risponderti, devo informarmi.
Before I answer you I must inform myself.
Concerning the sequence of tenses the same rules as mentioned before applies. To the simple infinitive corresponds the congiuntivo presente (the main sentence is in a present tense) or the congiuntivo imperfetto (the main sentence is in a paste tense). To the infinito passato corresponds the congiuntivo passato prossimo (the main sentence is in a present tense) or the congiuntivo piucheperfetto (the main sentence is in a past tense).