Structures that indicate the progression of an action, subject passivity, impersonality, and more. For example, I can say, 'adesso STO STUDIANDO'. This is an unfinished action that happens in the present, or I can say, 'Questa torta รจ stata fatta ieri', and this does not specify who made the cake, so it is a passive sentence. In this case of a 'passato prossimo'. Or I can say, 'si mangia!' This is a sentence without a subject and therefore impersonal