In English, it is customary to use the word necessary to form a general obligation in a sentence. In Spanish, the word forms used are rigid, and are not tenses. Obligational phrases do not command anyone to take action (this is what the imperative tense is used for), rather indicate an action that is to be done. There are three obligational forms in Spanish: the first is a general obligation to perform the action at hand, the second obligates a specific person to perform an action, and the third indicates a need or necessity for something - an essential need.
The first obligation form in Spanish is the general necessity to perform an action, without indicating who should perform it. The grammatical structure of the general obligation is:
1. The room must be cleaned Hay que limpiar la habitación 2. The dishes must be washed Hay que lavar los platos
Obligating a Designated Person to Take Action
The second form of obligation relates to a task that is to be done by a designated person. There are two grammatical possibilities for such: the first one uses tener que…’ and the second one uses the verb deber.
The first specific obligation structure:
The second obligation structure:
The meaning of ‘tener que’ is sronger than the meaning of ‘deber’, and can be compared to the use of ‘have to’ and ‘should’ in English.
1. You have to clean the room a. (Tú) Tienes que limpiar la habitación b. (Tú) Debes limpiar la habitación (You should clean the room)
2. You-all have to wash your hands a. (Uds.) Tienen que lavarse las manos b. (Uds.) Deben lavarse las manos (You-all should wash your hands)
The necessity for something
The final obligation form indicates a strong need (necessity or requirement) for something.
A structure indicating a strong need for something:
One must eat in order to live Hace falta comer para vivir