Impersonal necessity with bisogna
To talk about general rules or what "one must" do, Italian uses the impersonal expression bisogna.
Because it is impersonal, bisogna doesn't change to match a specific subject. It is always followed directly by an infinitive. This makes it perfect for discussing general obligations like the rules of the road.
| The speed limit is fifty, so one must slow down. | Il limite di velocità è cinquanta, allora bisogna rallentare. |
| One must always fasten the seatbelt in the car. | Bisogna sempre allacciare la cintura in macchina. |
To say "one must not" do something, place non before bisogna.
| Since there are some pedestrians, one must not overtake now. | Siccome ci sono alcuni pedoni, non bisogna sorpassare adesso. |
When using a reflexive verb, attach the pronoun si to the end of the infinitive, dropping the final -e.
| When a pedestrian crosses the street, one must stop. | Quando un pedone attraversa la strada, bisogna fermarsi. |
Other ways to state rules
You can express similar ideas using è (it is) plus an adjective, such as è importante (it is important) or è pericoloso (it is dangerous), followed by an infinitive.
| It is important to respect speed limits. | È importante rispettare i limiti di velocità. |
| It is dangerous to overtake another car here. | È pericoloso sorpassare un'altra macchina qui. |
Impersonal rules vs. personal obligations
Bisogna only works for general statements without a specific subject. To say that a specific person must do something, use the verb dovere (must) conjugated for that person, or simply conjugate the action verb normally.
| Pedestrians must be cautious when they cross. | I pedoni devono essere prudenti quando attraversano. |
| Why do you never fasten your seatbelt? | Perché non allacci mai la cintura? |
