Modals of Deduction (Present): Must, Might, Could, Can't

• When we guess about a present situation based on available evidence, we use modals of deduction. Our choice of modal depends on how certain we feel about the situation.
• Modal
• Certainty Level
• Meaning / Usage
• Example
• must
• 90–100% sure (positive)
• We are almost certain something is true.
• The truck speed is zero; the driver must be on a break.
• might / could
• 30–50% sure (possible)
• Something is possible, but we are not certain.
• The unit might be in a dead zone right now.
• can't
• 90–100% sure (negative)
• We are almost certain something is impossible.
• He can't be in Texas because his ping was in Ohio.
• Remember
• Use 'must + base verb' when you feel sure that something is true.
• Use 'might + base verb' or 'could + base verb' when something is possible but uncertain.
• Use 'can't + base verb' when you feel sure that something is impossible.
• Never use 'mustn't' for negative deduction; always use 'can't'.
• Examples
• The truck is moving at 65 mph, so the driver must be awake.
• The dispatcher could be on another call right now.
• Unit 204 can't be at the warehouse yet because of heavy traffic.
• Common mistakes
• He mustn't be at the terminal because his truck is here.
• He can't be at the terminal because his truck is here.
• The driver must to be in Chicago by now.
• The driver must be in Chicago by now.

Complete the sentences

• Unit 501 is moving at 70 mph towards Dallas. The driver (be) ____ awake.
• The trailer (not / be) ____ empty because the bill of lading shows 40,000 pounds.
• Sean cannot find the vehicle on his map. The driver (be) ____ driving through a mountain pass.
• It is 3:00 PM and the truck was due at 8:00 AM. The broker (be) ____ worried about the delay.
• The ELD shows zero driving hours left. The driver (not / continue) ____ without a rest break.
• The phone is ringing, but there is no answer. Mark (sleep) ____ in the sleeper berth.

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