The English “to be supposed to” has several meanings. It can express duty, expectation, plan, or belief. French does not use one single form for all of these. The choice depends on the sense in context.

obligation or duty

When “supposed to” means that someone has a duty or rule to follow, French often uses devoir.

• Tu dois finir ce travail. “You are supposed to finish this work.”
• Nous devons respecter les règles. “We are supposed to follow the rules.”
• Il doit appeler sa mère. “He is supposed to call his mother.”

In the past:

• Tu devais venir. “You were supposed to come.”
• Ils devaient arriver à midi. “They were supposed to arrive at noon.”

This use is very common and direct.

expectation or plan

When “supposed to” refers to what is planned or expected, devoir is again common, often in the imperfect or conditional.

• Le train doit partir à huit heures. “The train is supposed to leave at eight.”
• Elle devait nous rejoindre plus tard. “She was supposed to join us later.”
• Le film devrait commencer bientôt. “The film is supposed to start soon.”

The conditional (devrait) can soften the statement or show doubt.

what is said or believed

When “supposed to” means “it is said” or “it is believed,” French often uses être censé or impersonal forms.

être censé

être censé stresses what is officially expected or assumed.

• Tu es censé savoir ça. “You are supposed to know that.”
• Il est censé être expert. “He is supposed to be an expert.”
• Nous sommes censés partir demain. “We are supposed to leave tomorrow.”

Past:

• Elle était censée venir. “She was supposed to come.”

impersonal forms

French can also use impersonal phrases like on dit que or il paraît que.

• On dit qu’il est riche. “He is supposed to be rich.”
• Il paraît qu’elle vit ici. “She is supposed to live here.”

These shift the focus to what people say.

near future expectation

When the sense is that something is about to happen or expected soon, French may use the near future.

• Il va pleuvoir. “It is supposed to rain.”
• Nous allons recevoir une réponse. “We are supposed to get an answer.”

In the past:

• Il allait pleuvoir. “It was supposed to rain.”

This often overlaps with the idea of expectation.

strong expectation or likelihood

Sometimes “supposed to” means something is likely or expected based on logic. French may use the future or conditional.

• Il sera déjà là. “He is supposed to be there already.”
• Elle serait en retard. “She is supposed to be late.”

The conditional can suggest doubt or second hand information.

criticism or reproach

“Supposed to” can also carry a tone of blame. French often uses devoir or être censé in this case.

• Tu es censé m’aider. “You are supposed to help me.”
• Tu devais m’appeler. “You were supposed to call me.”

Tone and context make the reproach clear.

alternative expressions

French has several other ways to express similar ideas:

• être sur le point de for something about to happen
• être prévu de for something planned
• être attendu for something expected

Examples:

• Le train est prévu à huit heures. “The train is supposed to arrive at eight.”
• Il est attendu à midi. “He is supposed to arrive at noon.”
• Nous étions sur le point de partir. “We were supposed to leave.”

These are more specific and depend on context.

summary

• no single French form matches “to be supposed to”
• devoir is the most common choice for duty and plans
• être censé stresses what is expected or assumed
• impersonal forms express what people say or believe
• tense choice shows time and degree of certainty