Italian: Essere vs Stare

[Villa]

Italian essere vs stare. Looks a lot like ser and estar but they don't always go along with the Spanish ser vs estar rules of usage.

ESSERE AND STARE

While essere can be translated into English by using the verb to be, the other verb stare can either mean to stay (when used alone) or to be (when followed by an adjective or by a verb).
This page tries to focus when to use them correctly.

When followed by an adjective, essere expresses a quality, or a condition:
Lui è bravo = he is clever
Io ero stanco = I was tired
Loro saranno pronti = they will be ready or they may be ready (dubitative shade of meaning)
(voi) siete cordiali = you are cheerful

It is also used as an auxiliary verb in forming compound tenses of many intransitive verbs :
(io) sono venuto = I came (I have come)
(tu) eri tornata = you had come back
(noi) eravamo usciti = we had gone out
(essi) saranno cresciuti = they will have grown up, or they may have grown up

Since the verb essere lacks a past participle in forming compound tenses the past participle of stare, i.e. stato, is used as a replacement, including its feminine and plural forms stata, stati, state:
(io) sono (io) sono stato / stata = I am; I have been
(tu) eri (tu) eri stato / stata = you were; you had been
(voi) sarete (voi) sarete stati / state = you will be; you may have been

In the same way, the imperative tense of stare replaces the missing one of essere:
(tu) stà qui! = (you) stay here!
(tu) stà zitto! = (you) be quiet! = shut up!
(voi) state fermi! = (you plural ) stay still!

Stare is also used as an auxiliary verb before the gerund, either in the present, imperfect or future indicative tenses, as already discussed in paragraph
Lui/Lei sta mangiando = he / she is eating
(noi) stavamo dormendo = we were sleeping
(tu) starai leggendo = you will be reading, or you may be reading
(essi) staranno studiando = they may be studying

Besides the use as an auxiliary verb, in the spoken language stare commonly replaces essere to express the idea of somebody or something existing, resting, staying, remaining in a given place, almost to underline the static condition of the subject. In other words, stare describes the fact of being in some place as if this was an action, while essere describes it as a state, or a condition.
Both forms may be used, although the one with stare is more colloquial:
(io) sto qui ~ (io) sono qui = I am here
(tu) stai a casa ~ (tu) sei a casa = you are at home
(io) starò in Francia ~ (io) sarò in Francia = I will be in France
dove sta il mio bastone? ~ dov'è il mio bastone? (note the inverted subject) = where is my stick?
i giornali stanno sul tavolo ~ i giornali sono sul tavolo = the newspapers are on the table
in agosto staremo al mare ~ in agosto saremo al mare = in August we'll be at the seaside
le biciclette stavano nella rimessa ~ le biciclette erano nella rimessa = the bycicles were in the shed

Stare is more correctly used when expressing a physical position (but also in this case essere may be used as an alternative verb):
(essi) stanno seduti = they are sitting = they are staying seated
(noi) stavamo fermi = we were still = we were staying still
(ella) sta in piedi = she is standing
udendo quel rumore, il cane stette immobile = hearing that noise, the dog stayed still
il bambino stava carponi sul tappeto = the child was on his fours over the carpet

The verb stare is also commonly used to express and/or to inquire about health conditions (to be, to feel), either alone or followed by an adverb, such as the following ones:

bene (well, fine),
male (sick, not well),
meglio (better),
peggio (worse),
benissimo (very well),
malissimo (very bad),
and so on. In this case only stare can be used, while essere is NOT allowed:
come stai? = how are you? ~ how do you feel?
sto bene = I am (feeling) well
non stiamo troppo bene = we are not too well
stava male = he / she was feeling sick
domani starete meglio = tomorrow you will be (feel) better
ieri stavamo peggio = yesterday we were (feeling) worse
stanno ottimamente = they are (feeling) perfectly well

But when adjectives are used, such as malato (sick), depresso (depressed), allergico (allergic), etc., the only verb allowed is essere (i.e. the only verb that can be used with adjectives, to express a condition), and stare cannot be used.

Lui è malato = he is sick
Voi siete allergici = you are allergic
Io ero depresso = I was depressed
Lui è stordito = he is drowsy
eravate preoccupati? = were you worried?

So, talking about health (including a person's psychic condition), the two possible schemes are:

stare + adverb or essere + adjective

This does not override any of the aforesaid general rules, so the verb stare is also used in forming compound tenses:

sono depresso = I am depressed
sono stato depresso = I have been depressed

eravate ansiosi = you were anxious
siete stati ansiosi = you have been anxious

Be careful not to mistake adjectives, as the ones used in the previous examples, with the past participle of some verbs. Here the verb is shown in red (but not the adjective):

sono malato = I am sick
sono is the present tense of essere, and malato is a real adjective

sono guarito = I have recovered
sono guarito is the passato prossimo (present perfect) of guarire = to recover, whose past participle is guarito

erano depressi = they were depressed
erano is the imperfetto tense of essere; depressi is a real adjective

erano peggiorati = they had worsened
erano peggiorati is the trapassato prossimo (past perfect) of peggiorare = to worsen, whose past participle is peggiorato

The difference appears more clearly by reversing the tenses, i.e. by turning the first and third example into the same tenses used in the second and fourth sentences, and vice-versa.

sono malato (presente) = I am sick
sono stato malato (passato prossimo) = I have been sick

erano depressi (imperfetto) = they were depressed
erano stati depressi (trapassato prossimo) = they had been depressed

sono guarito (passato prossimo) = I am sick
guarisco (presente) = I recover

erano peggiorati (trapassato prossimo) = they had worsened
peggioravano (imperfetto) = they worsened

A further use of the verb stare is with the preposition per, followed by the infinitive of another verb. This expresses an action that is very close to happen (either in time or as a chance), usually translated in English as to be on the point of..., to be almost..., etc.:
il treno sta per partire = the train is on the point of leaving
(essi) stavano per rifiutare quel lavoro = they had almost refused that job
(io) sto per andare a letto = I am on the point of going to bed
(egli) è stato per morire = he was on the point of dying, he almost died
stanno per cominciare gli esami (note the postponed subject) = the exams are going to begin