Modals: Should and Ought

Sometimes we can use more than one word to express the same thing. Sometimes these words may be slightly different in their meaning and sometimes they mean exactly the same.

In this post I'll show you the case of "should" and "ought to".  Usually this words can be used with almost no difference in meaning, but of course there are cases were you can use both and cases that only one of them would be appropriate and even cases where none of them will be correct. The following study was taken from the "Advanced Grammar in Use" by Martin Hewings, Cambridge Press University.

Usually we use "should" or "ought to" to express:

• Obligation and probability
  
  
  
  • Obligation
    We can either use "should" or "ought to" to give advice or recommend something that we believe is the best thing to do.
    Example: This car is way too expensive. You should/ought to look for another one.
    
    NOTE: Sometimes "should" or "ought to" are not the best option and other words are more suitable. There are also cases when only one of these two words is suitable. So let's see all different cases:
    
    
    
    
    • For an outside authority recommendation
      Sometimes we need to say what an outside authority recommends; in that case it is preferable we use "should” instead of "ought to".
      Example: "In the Department of Immigration and Foreign Affairs website says all documents written in a foreign language should be translated by a NAATI accredited translator."
      
      
    • For an advice using I
      When we are giving advice to someone and we use I, then we can't use "ought to", and we have to use "should" or "would".
      Example: I should save some money for a rainy day, if I were you. (could also be "I would save ... " or "I'd save ... "
      
    
    
    
    
    
  • Responsibility or duty
    We use "should" or "ought to" to express duty or responsibility.
    Example: People should/ought to be warned that dumping rubbish in the common areas is not aceptable.
    
    
  • Probability
    We also use "should" or "ought to" to express probability of something being true in the present or near future.
    Example: You should/ ought to have received the invitation by now.
    
  
  
  
  
  
• Obligation in the past or expectation in the past or near future
  
  
  
  • Obligation in the past (usually showing some regret or criticism)
    Sometimes we used "should" or "ought to" followed by the verb in the present perfect when we want to talk about an obligation in the past that usually indicates some criticism or regret.
    Example: He should/ought to have asked me if I was available before offering my services to someone else. (I'm so annoyed)
    
    
  • Expectation that something happened or will happen.
    When we are expecting that something happened or is going to happen in a near future we can also use "should" or "ought to" followed by the present perfect.
    Example: "If there was no delays, he should/ought to have arrived in Canberra this morning."
    
  
  

In some cases, speacially in spoken English, other words are prefered to "should" or "ought to".

• To say it would be sensible or advisable to do something
  When we want to say someone that we believe it would sensible or advisable for them to do something, we can use "had better" instead or "should" or "ought to".  
  Example: "If you can't help her with the job, you'd better tell her."
  NOTE: We DO NOT use "had better" to talk about the past or to make general comments.
  Example: I don't believe parents should/ought to give their kids sweets.
  
  
• To express an obligation to do something (less strong obligation)
  We can also use "(be) supposed to" instead of "should" or "ought to" to talk about an obligation to do something, usually a less strong one.
  Example: I'm supposed to finish this report in 20 minutes.
  

In other cases "should" or "ought to" aren't suitable at all and other options must be used

• Making a logical conclusion
  When we are making a logical conclusion about a situation or activity we can't use "should" or "ought to", we use "must" instead.
  Example: She must be out of her mind if she thinks I'll keep on paying her bills.
  

Kangas