| Expressing Certainty | Expressing Uncertainty |
| I’m sure (certain/positive) that… Yes, definitely (certainly/of course). There is no doubt… undoubtedly It is obvious (evident/crystal clear) that… No one can deny that… | It’s possible. It might be. It could happen. I suppose, but I wouldn’t like to say for certain. I’m not sure. I doubt it. It’s doubtful. It’s very unlikely. You never know, of course. No one can know for certain. I can’t tell you for sure. |
| There is no doubt that John will pass his driving test. I’m sure that many of us today can’t spend a day away from our mobile phones. | I can’t tell you for sure. I think he still needs some practice. I doubt that. |
