• Perfect Modals: Should Have

• 
• Use the perfect modal form of should to show regret* or judgement** about actions/events in the past.

  
  

  subject + should + have + past participle

  
  

  -I should have studied medicine. (But I didn't.)

  (This shows regret because the person is upset they did NOT study medicine. They studied a different subject.)
  

  
  

  -John should have studied medicine. (But he didn't.)

  (This shows judgement because the person has an opinion about John and the subject he studied.)

• They should have joined a study group.

  He should have carried his own books.

• *Regret: to feel sad or sorry about something you did or did not do

  **Judgement: to form an opinion about someone or something

Source : Alison