1. As a necessity:
* Il faut (formal) - This is the most common and versatile translation. It means "it is necessary," "one must," or "you must."
* Il est nécessaire de (formal) - More formal and translates to "it is necessary to."
* Il est indispensable de (formal) - Even more formal, meaning "it is indispensable to."
* On doit (informal) - Less formal, means "one must" or "we must."
* Il est important de (formal) - "It is important to"
2. As an obligation:
* Il faut (formal) - Also used for obligations, meaning "you must" or "one must."
* On doit (informal) - "One must" or "we must."
* Il est obligatoire de (formal) - "It is obligatory to."
3. As a strong suggestion or advice:
* Il faut (formal) - Can be used to express a strong suggestion, meaning "you should."
* Il serait bon de (formal) - "It would be good to."
4. As a certainty:
* Il doit (formal) - This translates to "he/she/it must" and expresses certainty.
Example:
* Il faut que j'aille au magasin. (I must go to the store.)
* Il est nécessaire d'apprendre le français. (It is necessary to learn French.)
* On doit respecter les règles. (One must respect the rules.)
* Il doit être à la maison. (He must be at home.)
Important Note: The choice of translation depends on the context and the desired level of formality.