Modals of Deduction (Past)

• We use past modals of deduction when we want to make guesses or draw conclusions about things that happened in the past. The choice of modal verb shows how certain we are about our guess.
• Modal of Deduction
• Degree of Certainty
• Example
• must have + past participle
• Almost certain (positive)
• Jessica must have deleted the file.
• might have / could have
• Possible
• Mark might have changed the server settings.
• can't have / couldn't have
• Almost certain (negative)
• David couldn't have seen the audit log.
• Remember
• Use must have when you are very sure something happened based on evidence.
• Use might have or could have when you think something is possible, but you are not sure.
• Use can't have or couldn't have when you are sure something did not happen.
• Always use the past participle of the main verb after have.
• Examples
• The database crashed, so someone must have run the wrong query in Boston.
• Brian wasn't in the office in Seattle, so he couldn't have caused the outage.
• Sarah didn't reply to my email, so she might have left her laptop at home in Chicago.
• Common mistakes
• Kevin must left the server running in London.
• Kevin must have left the server running in London.
• Rachel can't missed the confirmation dialog in Dallas.
• Rachel can't have missed the confirmation dialog in Dallas.

Complete the sentences

• The marketing folder is gone, so someone ___ (delete) it by mistake. (delete) ____
• Kevin's laptop is still in Seattle, so he ___ (travel) to New York yet. (travel) ____
• The audit log is empty, meaning an admin ___ (wipe) the records. (wipe) ____
• Lisa is on holiday in Denver, so she ___ (access) the database last night. (access) ____
• The system rebooted suddenly, and a power surge ___ (cause) it. (cause) ____
• Brian knew the password, so he ___ (log) in without any issues. (log) ____

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