Imperfect systems and diachronic change
Syntactic change consists of (a series of) small, local changes which are the result of chance or are brought about by the possible imperfections of the linguistic system — the impression of globality of the change is due to the sum of the individual changes which, eventually eliminating single imperfections, contribute to the formation of a more coherent system. In Modern Italian, one can identify two independent reflexive (“<i>si</i>”) constructions which syntactically demote the lexical subject: a passive one and an impersonal one, with quite distinct properties. Old Italian only had passive <i>si </i>— the impersonal construction is the result of many small changes in the rules and the domain of application of the passive construction: these changes began in the Old Italian period and lasted for at least five centuries. But this new construction, not being the result of a unitary project, continues to show signs of being imperfectly put together.