22.214.171.124.1 the passato prossimo if there is a modal verb
If there is a modal verb and the main verb isn't reflexive, the auxiliary verb to be used (essere / avere) depends exclusively on the main verb. If the main verb is conjugated normally with avere it is conjugated with avereï¿½and if it is conjugated normally with essere it is conjugated with essere. This may seem very logical and it is very logical indeed. (We just mention it for the people who speaks French because in French it is different. If there is a modal verb the conjugation is with avoir regardless which auxiliary very is used normally.)
If there is a modal verb and the main verb is reflexive a distinction is to be made. If the reflexive pronoun is in front of the auxiliary verb the verb is conjugated with essere. But if the reflexive pronoun is added to the infinitive (in the case that there is a modal verb there is an infinitive as well) the auxiliary verb to be used depends on the main verb. If the main verb is conjugated normally with avere it must be conjugated withe avere, otherwise with essere.
reflexive pronoun in front of a modal verb (the reflexive pronoun can be dative or accusative)
verbes with accusative
lavare (to wash)
costruire (to construct)
vedere (to see)
scusare (to apologize)
verbis with dative
permettere (to allow)
dare (to give)
Mi sono dovuto costruire una casa. <=> I must have built a house for myself.
Ci ha voluto dare la sua macchina. <=> He wanted to give us his car. (not reflexive!)
Ce lo siamo voluto permettere. <=> We wanted to allow it to us.