Passive voice with si

-->

This kind of passive is formed with si + 3th person singular or plural of the verb. In this case the sentence has a general meaning (everybody, people etc.)In Spagna si mangia paella.
When the passive subject is singular the verb is conjugated in the 3th person singular, instead when the passive subject is plural the verb is conjugated in the 3th person plural, example:

La mattina spesso si beve il caffè (il caffè: singular)
in Italia il giovedì si mangiano gli gnocchi (gli gnocchi: plural)

With this form of passive voice the agent is not expressed.

Paolo mangia gli spaghetti (active voice)
~~Gli spaghetti si mangiano da Paolo~~ (it has not the same meaning!!! It means: a casa di Paolo si mangiano gli spaghetti!)
But with the same meaning of the active voice sentence, we can say:
Gli spaghetti sono mangiati (or vengono mangiati) da Paolo.