Should, Ought and Must

Should and ought have similar meanings. They are both used to talk about obligation, and to give advice or instructions.

• We should respect our parents.
• We ought to respect our parents.
• You should stop smoking.
• You ought to stop smoking.
• I think you should go to university.
• You should talk to the manager.
• He ought to work harder.
• We ought to find a solution.

Must is stronger than should and ought.

• You must stop smoking. (A command.)
  
• You should/ought to stop smoking. (A piece of advice.)
  
• You must send the payment immediately.
• I must get that tooth extracted.
• Vehicles must not be parked in front of the gate.
• You must not waste money on useless things.

Must expresses certainty. Should/ought to expresses probability.

• He must be home now. (It is certain.)
  
• He should be home now. (It is probable.)
  

Sections in this article

Will as a modal auxiliary verb
Would as a modal auxiliary verb
Could as a modal auxiliary verb