> For the complete documentation index, see [llms.txt](https://viktor-8.gitbook.io/untitled/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://viktor-8.gitbook.io/untitled/english/speculation-and-deduction.md). # Speculation and deduction Modal verbs and expressions ## Modal verbs of speculation and deduction ### Must We use **must + infinitive** for obligation and strong recommendation, but also to say that we are **quite sure that something is true**. * *They are almost identical. They **must*** ***be** sisters.* * *But I answered all the questions correctly. There **must be** a mistake.* We use **must be** + –**ing** with dynamic verbs to say that we are quite **sure that something is happening now**. * *What you are saying is not possible. You **must be kidding**.* * *Can you hear the shouting? Our neighbours **must be arguing** again.* We use **must have + past participle** or **must have been + -ing** to say that we are quite sure that something **was true or happened in the past**. * *I can’t find my wallet! I **must have dropped** it in the taxi.* * *You **must have had*** *a real scare when you saw the crocodile.* * *He was the only victim. He **must have been sleeping*** *when the fire started.* ### Can’t We can use **can’t + infinitive** to say that we are **quite sure that something is NOT true**. * *He **can’t be** that famous. I’ve never heard his name before.* * *She **can’t be** married. I have never seen a ring on her finger.* We use **can’t be** + –**ing** to say that we are quite **sure that something is NOT happening now**. * *They **can’t be travelling** by bus. There is no bus service on Sundays.* We use **can’t/couldn’t have + past participle** or **can’t have been + -ing** to say that we are **quite sure that something did NOT happen or was NOT true in the past**. * *You **can’t/couldn’t have seen** John last night. He was in hospital.* * *She **can’t/couldn’t have passed** the test. She didn’t even open the books.* Note that for negative deduction we use **can’t** and NOT ~~**mustn’t**~~ * *He **can’t be** that famous.* (NOT ~~*He mustn’t be that famous*~~*.*) ### **Could/might/may** We can use **could/might/may + infinitive** to say that **it’s possible that something is true** (but we are not sure). * *I can’t get hold of him on the phone. He **could/might/may be** away.* * *We didn’t do anything when we could and now it **could/might/may be*** *too late.* We use **could/might/may be** + –**ing** to say that we are quite **it’s possible that something is happening now** (but we are not sure). * *Tom isn’t at the office. He **might/may be working** from home today.* * *‘Why isn’t she picking up her phone.’ ‘She **might/may be driving****.’*** We can use **could/might/may have + past participle** or **might/may have been + -ing** to say that **it’s possible that** **something was true or happened** in the past. * *It’s been three days. They **could/might/may*** ***have finished** painting the house by now.* * *If they left at 9, they **could/might/may have*** *already* ***arrived**.* * *She was home last night but didn’t answer the door. She **might/may have been having** a shower.* We can use **could have + past participle** to say that something was possible in the past but did not happen. * *He **could have played** in the first division, but he had a terrible injury.* * *He **could have had** better jobs if he had spoken English.* Note that we use **might not** or **may not** (NOT ~~**could not**~~) to talk about a negative possibility. * *He seems too calm. He **might/may*** ***not be** aware of the risks.* * *She **might/may not have heard** us. Knock again.* ### **Should/ought to** We use **should**/**ought to + infinitive** to talk about a situation that we expect to happen (present or future). * *He **should/ought to be** home by now. He is always home before 7.* * *They **should/ought to arrive** before midnight.* We use **should have**/**ought to have + past participle** to talk about a situation expected to happen in the past. We can also use this form to express criticism. * *He **should/ought to*** ***have received** the parcel yesterday. I sent it two days ago.* * *He **should/ought to have studied** more. Nobody fails if they study.* ### Expressions for speculation ### **Bound/sure** **Bound** and **sure** are adjectives that are used to say that we are quite sure that something will be true or happen. We use them in the structure **be bound/sure + to**-infinitive. * *The Jamaican **is*** ***bound/sure*** ***to win** the final.* * *There **are bound/sure*** ***to be** some discrepancies during the meeting, so be prepared.* ### **Likely/unlikely** **Likely** and **unlikely** are adjectives. If something **is likely to happen** it means that it will probably happen or that it is expected to happen. If something **is unlikely to happen** it means that it probably won’t happen. We can use these two adjectives in two ways. **It is likely/unlikely that** + clause * ***It’s likely that** just in a few years we will change our economic model.* * ***It’s unlikely that** the police had anything to do about it.* Subject + **be likely/unlikely** + **to** + infinitive * *He **is likely to** win this game.* * *They **are unlikely to** reach an agreement.* ### **Definitely/probably** **Definitely** and **probably** go before the main verb and after the auxiliary verb (if there is one) in (+) sentences. * *You’**ll*** ***definitely** get the job. Nobody’s got your qualifications and experience.* * *He’**s definitely** our best player.* And they go before the auxiliary verb in (-) sentences. * *They* ***definitely won’t find** any evidence.* * *She **definitely isn’t seeing** anyone right now.*