6.7 The formation of the passato prossimo with a modal verb
In Italian the formation of passato prossimo with a modal works different from English.
Ho potuto farlo.
In other words, you build the passato prossimo with the past participle of the MODAL VERB and you add to the main verb in infinitive. The auxiliary verb to be used, essere in the case of an intransitive verb (we already mentioned that we simplify, we are going to talk about that again later) and avere in the case of a transitive verb.
intransitive verb Sono potuto venire. => I have been able to come. transitive verb Ho potuto comprarlo. => I have been able to buy it.
In other words it depends on the main verb whether essere or avere is to be used. We say that for all of you who speak French, because it is not as in French. In French you have to conjugate with avoir (avere) in this case, regardless wheter the main verb is conjugated normally with essere / être or with avoir / avere.
intransitive verb: avoir in French / essere in Italian
French: J'ai pu venir.
Italian: Sono potuto venire.
transitive verb: avoir in French / avere in Italian
French: J'ai pu l' acheter.
Italian: Ho potuto comprarlo.
Don't mind if that is not yet clear. We are going to discuss the topic once again later.