Grammar: Modals of Deduction (Past & Present)

Use modals to make logical guesses or deductions about a situation based on evidence, expressing a degree of certainty.

Form: `modal + base verb` Must (95% certain): The lights are on. He must be home. Might / May / Could (50% certain): She isn't answering her phone. She might be in a meeting. Can't (99% certain it's impossible): He just left 2 minutes ago. He can't be at the airport already.

Form: `modal + have + past participle (V3)` Must have (95% certain): The ground is wet. It must have rained last night. Might / May / Could have (50% certain): He's late. He might have missed the bus. Should have (Expresses regret or criticism): I should have studied harder for the test. Couldn't / Can't have (99% impossible): She didn't study at all. She can't have passed the exam.