Expressing certainty and uncertainty (B1 Vocabulary)

Say I'm sure or the stronger, more formal I'm certain when you have good reason to believe something is true.

Sounding sure

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 ___ that the figure is right. Choose the word for the blank. (certain / maybe / probably) Answer: certain — I'm certain shows full, formal confidence; "maybe" and "probably" show doubt.

Word	Pronunciation	Example
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.

Use definitely when you have no serious doubt and probably when something is likely but not certain, usually before the main verb.

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: I'm not sure, but it will ___ arrive soon. Choose the word for the blank. (probably / definitely / certainly) Answer: probably — He says he's not sure, so his guess takes probably, not "definitely" or "certainly".

Word	Pronunciation	Example
definitely	/ˈdefɪnətli/	Yasmin will definitely attend the workshop.
probably	/ˈprɑbəbli/	Matilda is probably at the animal clinic right now.

Use I think or maybe to soften a guess and leave room to be wrong.

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. ___ it starts at seven. Choose the words for the blank. (I think / I'm certain / Definitely) Answer: I think — She isn't sure, so I think softens it; "I'm certain" claims full confidence.

Word	Pronunciation	Example
I think	/aɪ θɪŋk/	I think Lani is waiting near Ghafwick Station.
maybe	/ˈmeɪbi/	Maybe we should meet at Magaff Library instead.

Incorrect	Correct	Why
"The meeting starts at two." (stated as plain fact, no room for doubt)	"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.
Guessing, you say: 'The bus definitely comes in ten minutes.'	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.
"You sent the email to the wrong address." (sounds like an accusation)	"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.