One statement, three strengths
Modal verbs in the condizionale take the edge off a statement. This works in two directions: certainty, how sure you are, and pressure, how strongly you ask for something. At this level the point is choosing the right strength.
From certain to open
Marta è a casa.
Marta is at home.
A fact.
Marta deve essere a casa.
Marta must be at home.
A firm conclusion: the light is on.
Marta dovrebbe essere a casa.
Marta should be at home.
An expectation: that's where she usually is.
Marta potrebbe essere a casa.
Marta could be at home.
One possibility among several.
Grading certainty
dovrebbe is the step you need most: you expect something without committing to it. It lines up neatly with English should, as in It should be ready by now. potrebbe leaves the question open, like might or could. For the past, add the past infinitive: dovrebbe essere arrivato.
The scale
| Form | English | Stance |
|---|---|---|
| deve | must | You conclude it from evidence. |
| dovrebbe | should, ought to | You expect it. |
| potrebbe | could, might | You think it possible. |
In everyday life
Il pacco dovrebbe arrivare domani.
The parcel should arrive tomorrow.
A quest'ora dovrebbe essere già partito.
By now he should already have left.
Potrebbe trattarsi di un errore del sistema.
It might be a system error.
Deve aver dimenticato le chiavi in ufficio.
He must have left his keys at the office.
Grading pressure
Requests follow the same scale. With deve you give an instruction, with dovrebbe you state an expectation, and potrebbe as a question makes a request. The impersonal forms sound even more reserved because they address no one directly: bisognerebbe, converrebbe, si dovrebbe.
The same request to a client
Direct
Deve mandarmi il contratto entro venerdì.
You must send me the contract by Friday.
Sounds like a rule.
Bisogna rivedere il budget.
The budget needs revising.
Softened
Potrebbe mandarmi il contratto entro venerdì?
Could you send me the contract by Friday?
A request.
Bisognerebbe rivedere il budget.
The budget ought to be revised.
potrebbe has both readings. As a question it is a request: Potrebbe richiamarmi domani? As a statement it names a possibility: Potrebbe richiamare domani.
Holding back your own view
In conversation you also put the condizionale on the verb that carries your own stance. Disagreement and doubt then sound like an offer rather than a verdict. English does this with I'm not so sure or I'd have my doubts; Italian uses the conditional far more often.
Disagreeing without friction
Non sarei così sicuro.
I wouldn't be so sure.
Avrei qualche dubbio sui tempi.
I'd have a few doubts about the timing.
Sinceramente non saprei.
Honestly, I couldn't say.
Mi permetterei di aggiungere una cosa.
If I may, I'd like to add one thing.
