Saying what everybody does
You eat well in Italy. There is no smoking here. How do you say that? — statements about people in general, with nobody in particular meant.
English improvises with whatever is at hand: generic you, formal one, vague people or they, or a passive. Italian needs none of that. It puts si in front of a verb in the third person singular — that is the si impersonale. One form, no register decision, no subject.
Three sentences that show the whole thing
In Italia si mangia bene.
In Italy you eat well.
Qui non si fuma.
There is no smoking here.
Come si dice „homesick“ in italiano?
How do you say “homesick” in Italian?
Habits, rules, advice
You will hear the si impersonale all the time: when someone says what is usual in a country, what the rules require, or what you do in a given situation.
In Spagna si cena molto tardi.
In Spain people have dinner very late.
In biblioteca non si parla ad alta voce.
You do not talk out loud in the library.
Con questo caldo si beve molta acqua.
In heat like this you drink a lot of water.
With modal verbs, si sits in front of the conjugated verb and the infinitive follows unchanged: si può, si deve, si dovrebbe, non si può. Italian notices keep an ordinary sentence and just leave the subject out, where English has no entry or booking required.
Can, may, must
Da qui non si può vedere il mare.
You cannot see the sea from here.
Si deve prenotare in anticipo.
You have to book in advance.
Si dovrebbe chiamare prima di passare.
You should call before dropping by.
The adjective goes plural
The verb stays singular, but an adjective or noun after essere, diventare or sembrare goes into the plural: everybody is meant, and the adjective is where Italian says so. Picture si as covering a crowd: the verb does not see the crowd, but the adjective does.
The plural in a sentence
Quando si è stanchi, si sbaglia di più.
When you are tired, you make more mistakes.
Quando si è giovani, si pensa di avere tempo.
When you are young, you think you have time.
Quando si è genitori, si dorme poco.
When you are a parent, you do not sleep much.
In vacanza si è più rilassati.
On holiday you are more relaxed.
Reflexive verbs — si si becomes ci si
A reflexive verb already carries a si of its own: si alza. Add the impersonal si on top and two identical syllables collide. Italian solves it by turning the first one into ci. English gets up and gets dressed with no reflexive pronoun, so the double si may look like one too many; it is not. This ci has nothing to do with the ci of place.
The workaround
ci si in everyday use
In campagna ci si alza presto.
In the countryside you get up early.
Con questo freddo ci si veste a strati.
In cold like this you dress in layers.
Alle feste ci si diverte sempre.
You always have fun at parties.
Si dice che — reporting what people say
si dice che, si pensa che, si crede che and si sa che report what is generally said or known without naming a source — the Italian equivalent of they say, it is thought, everyone knows.
After si dice che, si pensa che and si crede che the usual mood is the Congiuntivo: they float an assumption rather than state a fact. English gives you the opposite reflex, because they say it is expensive is plain indicative; in everyday speech you will also hear the Indicativo after si dice che. After si sa che the mood is the Indicativo, because it claims knowledge.
Si dice che sia caro ma molto buono.
They say it is expensive but very good.
Si pensa che il museo apra a giugno.
People think the museum opens in June.
Si sa che il traffico peggiora d'estate.
Everyone knows the traffic gets worse in summer.
Non si sa mai.
You never know.
In the past it takes essere
In the passato prossimo the impersonal si always takes essere as its auxiliary — including with verbs that normally want avere: not si ha mangiato but si è mangiato. English has only one auxiliary, so nothing warns you here.
With verbs that normally take avere, the participle stays singular: si è mangiato. With verbs that normally take essere, and with reflexive verbs, it is plural: si è partiti, ci si è alzati.
The past in a sentence
In quel posto si è mangiato davvero bene.
The food at that place was really good.
Si è arrivati tardi per colpa del traffico.
We got there late because of the traffic.
Ieri ci si è alzati prestissimo.
Yesterday we got up very early.
