What you'll learn
By the end of this lesson, you'll be able to express different degrees of certainty with the right words and modals.
When do I use it?
Choose your level of certainty:
- Absolute: "It is certain that...", "There is no doubt that...", "definitely", "certainly".
- High (deduction): "must", "surely": "She must be tired." "Surely you're joking."
- Strong belief: "I'm (pretty) sure that...", "I'm convinced that...".
Compare: "I'm sure he's lying" (belief) vs "He must be lying" (deduction from evidence) vs "It is certain that he's lying" (no doubt claimed).
How do I form it?
It is certain/clear/obvious + that + clause subject + must + base verb definitely / certainly + verb
- It is certain that prices will rise.
- There is no doubt that she works hard.
- He must have the wrong address.
- The plan will definitely succeed.
Common mistakes for Spanish speakers
Spanish "seguro que" is often said as "sure that" ("seguro que vendrá" → "sure he will come") — add the "I'm": "I'm sure he'll come". And "debe de" for probability is NOT "should" — use "must": "debe de ser verdad" = "it must be true". Do not over-claim: "certainly" and "definitely" are strong; use "probably" when you are not fully sure.
must + verb for deduction; definitely/certainly for strong claims; I'm sure that for belief.
Practice
Multiple Choice
C1Which sentence expresses deduction, not belief?
Fill in the Blank
C1There is no that she is talented.
Hint: 'There is no doubt that...' expresses absolute certainty.
Find the Error
C1Multiple Choice
C1Which adverb means 'without doubt'?
Practice Speaking
Apply what you've learned in a real conversation with AI feedback.
Level: C1