Expressing certainty and uncertainty (B1 Vocabulary)
When you feel confident, say I'm sure or, more formally and even stronger, I'm certain. Both go before that + a clause: "I'm sure (that) she left." Use them when you have good reason to believe something is true.
Sounding sure
I'm sure /aɪm ʃʊr/ — I'm sure Amina saved the file before she left.
I'm certain /aɪm ˈsɜrtn/ — Mei is certain the answer is correct.
Not ""The meeting starts at two." (stated as plain fact, no room for doubt)" — say ""I'm sure the meeting starts at two."". I'm sure signals it's your confident belief, not an official fact. It sounds friendlier and is safer if you turn out to be wrong.
Try it: Lars: Are you confident the figure in the report is right? Mei: Yes. I'm ___ the figure is correct. Which reply shows full, formal confidence? (certain / maybe / probably) Answer: certain — 'I'm certain' is the strong, formal way to show full confidence, which fits a report. 'Maybe' and 'probably' both signal doubt, so they weaken the very confidence she wants to show.
Definitely and probably
Definitely means 'certainly, with no serious doubt'. Probably means 'likely, but not 100%'. Both usually sit just before the main verb: "will definitely come", "is probably rehearsing". Definitely = very sure; probably = fairly sure.
definitely /ˈdefɪnətli/ — Yasmin will definitely attend the workshop.
probably /ˈprɑbəbli/ — Matilda is probably rehearsing at the theater right now.
Not "Guessing, you say: 'The bus definitely comes in ten minutes.'" — say "Guessing, you say: 'The bus probably comes in ten minutes.'". Match the word to what you know. Definitely claims no doubt; when you are only guessing, use probably.
Try it: Sofia: Do you know when the bus comes? Diego: Not the exact time, but it will ___ arrive soon. Which reply fits a careful guess? (probably / definitely / certainly) Answer: probably — 'Probably' fits because the bus is likely but not guaranteed to be soon, and he does not know the exact time. 'Definitely' and 'certainly' both claim there is no doubt, which is too strong for a guess.
Softening with I think and maybe
When you're not sure, soften your statement. I think introduces a belief or opinion: "I think Lani is waiting." Maybe means 'perhaps' and usually starts the sentence: "Maybe the cafe is closed." Both leave room for you to be wrong.
I think /aɪ θɪŋk/ — I think Lani is waiting near Ghafwick Station.
maybe /ˈmeɪbi/ — Maybe we should meet at the community center instead.
Not ""You sent the email to the wrong address." (sounds like an accusation)" — say ""Maybe you sent the email to the wrong address."". Maybe softens a guess so it feels like a suggestion, not a firm claim. It is much gentler when you're unsure.
Try it: Amina: What time is the concert? Camila: I didn't check the ticket, but ___ it starts at seven. Which reply sounds natural when she isn't sure? (I think / I'm certain / it definitely) Answer: I think — 'I think' introduces it as her belief and leaves room for doubt, which is exactly what she wants. 'I'm certain' and 'it definitely' both claim full confidence, which contradicts the fact that she is not sure.