When English speakers talk about events or ideas, they often signal how sure they are. The new policy will definitely succeed shows full confidence. The new policy will probably succeed shows high confidence. The new policy will possibly succeed shows lower confidence. The new policy might fail shows even less. Each word matches a different level of certainty. Students who use only sure and maybe miss most of the range. They also often confuse the words: saying I am certain when they mean probably, or using maybe when they should use possibly. This lesson covers the main certainty words at B1 level — sure, certain, definitely, probably, likely, possibly, perhaps, maybe — and shows how to teach them as a clear scale. Once students know the scale, they can choose the right word for the right level of confidence and sound more accurate.
Before you start — think honestly about your own teaching and experience.
Look at the examples. Answer each question before reading the explanation — this is how your students will learn too.
100% — definitely, certainly — She will definitely come to the meeting.
90% — probably, likely — She will probably come to the meeting.
50% — possibly, maybe, perhaps — She will possibly come to the meeting.
20% — possibly (lower) — She might possibly come.
0% — definitely not — She will definitely not come.
Look at the scale. What is the difference between will, will probably, will possibly, and might?
Each word on the scale matches a different level of certainty. Will alone signals strong confidence — close to 100%. Definitely makes that confidence explicit. Will probably is high but not full confidence — about 80% to 90%. Will possibly is lower — about 50%. Might (or could) is even lower — closer to 30% or 40%. The negative side works the same way: will definitely not is full confidence the thing will not happen; will probably not is high confidence; might not is lower. Students need to learn that confidence in English is not just yes or no — it has a scale, and the right word matches the speaker's actual confidence. Choosing definitely when only probably is true makes the speaker sound overconfident; choosing maybe when probably is true makes them sound more uncertain than they really are.
I am sure she will come. (everyday confident)
I am certain she will come. (slightly more formal, sometimes stronger)
Are you sure? (everyday)
Are you certain? (slightly more formal — used when checking carefully)
It is sure to rain today. ✗ (not natural English)
It is certain to rain today. ✓ (natural English)
When are sure and certain interchangeable, and when are they different?
Sure and certain mean similar things but are not always interchangeable. Both work after I am: I am sure and I am certain are both natural, with certain being slightly more formal. But in some patterns, only one works. It is certain to rain (not it is sure to rain) is the natural form for predicting future events with high confidence. He is sure of himself (meaning confident) does not work with certain — he is certain of himself sounds odd. For the most useful B1 patterns, students should learn I am sure / I am certain as everyday confident statements (with certain slightly more formal), and use it is certain that for predictions. The two words overlap but each has its own typical contexts.
Maybe she will come. (informal, conversational)
Perhaps she will come. (slightly more formal)
Possibly she will come. (formal or careful)
Maybe is at the start of the sentence. Possibly can be at the start or in the middle.
Maybe she is right. (start)
She maybe is right. ✗ (wrong — maybe does not go in the middle)
She is possibly right. ✓
She will possibly come. ✓
What is the difference between these three words, and what are the position rules?
Maybe, perhaps, and possibly all signal medium uncertainty (around 50%) but they differ in register and in where they can go in the sentence. Maybe is informal and goes at the start of the sentence (Maybe she will come). Perhaps is slightly more formal, also at the start, and is common in writing. Possibly is the most flexible — it can go at the start (Possibly she will come) or in the middle, like other adverbs (She will possibly come / She is possibly right). Students often try to use maybe in the middle of a sentence and produce wrong English. The position rule for maybe is fixed — it goes at the start. For middle positions, possibly is the right choice.
| Word | Approximate certainty | Register | Typical position |
|---|---|---|---|
| definitely | 100% — full confidence | Neutral, common | Middle of sentence: She will definitely come. |
| certainly | 100% — full confidence | Slightly more formal than definitely | Middle: She will certainly come. Or start: Certainly she will come (slightly old-fashioned). |
| sure | ~95% — confident | Everyday | After I am: I am sure she will come. |
| certain | ~95% — confident, slightly more formal | Slightly more formal than sure | After I am or it is: It is certain that she will come. |
| probably | ~80% — high confidence | Neutral | Middle: She will probably come. |
| likely | ~70% — high confidence, often in writing | Slightly more formal | Predicate: It is likely that she will come. / She is likely to come. |
| possibly | ~50% — medium uncertainty | Neutral | Start or middle: Possibly she will come. / She will possibly come. |
| perhaps | ~50% — medium uncertainty | Slightly more formal than maybe | Start: Perhaps she will come. (Common in writing.) |
| maybe | ~50% — medium uncertainty | Informal, conversational | Start only: Maybe she will come. |
| might / could | ~30-40% — lower probability | Neutral | Modal verb position: She might come. |
DISTINCTION 1 — The certainty scale: Definitely (100%) → probably (80%) → possibly (50%) → might (30%). Each word matches a level of confidence. Students who use only I am sure and maybe miss the middle of the scale and sound either overconfident or unsure when they should not.
DISTINCTION 2 — Sure vs certain: Both mean confident. Sure is everyday and slightly less formal. Certain is slightly more formal. After I am, both work: I am sure / I am certain. After it is, only certain is natural: It is certain that she will come (not It is sure that). For most B1 use, the two are interchangeable in I am... statements.
DISTINCTION 3 — Probably vs likely: Both mean high but not full confidence. Probably is more conversational and goes in the middle of the sentence (She will probably come). Likely is slightly more formal and often appears in predicate phrases (It is likely that she will come / She is likely to come). Students who only know probably can add likely for variety in writing.
DISTINCTION 4 — Possibly vs perhaps vs maybe: All signal around 50% certainty. Maybe is the most informal and only goes at the start of a sentence. Perhaps is slightly more formal, also at the start, common in writing. Possibly is the most flexible — start or middle. The position rule matters: Maybe she is right (correct) but She maybe is right (wrong).
DISTINCTION 5 — Position of certainty adverbs: Most certainty adverbs (definitely, certainly, probably, possibly) go in the middle of the sentence — between the subject and the verb (or after the modal/auxiliary). She will probably come. He has definitely arrived. Putting the adverb at the start (Probably she will come) is grammatically possible but sounds less natural than the middle position. Maybe is the exception — it goes at the start only.
Certainty words are essential for clear communication, especially in academic and professional contexts. A student who says All teenagers love social media when they only mean Many teenagers probably enjoy social media is making a stronger claim than the evidence supports. Choosing the right level of certainty matches the language to the actual level of confidence — and that is part of being taken seriously. At B1 level, students should learn to distinguish at least four levels: full certainty (definitely / certainly), high confidence (probably / likely), medium uncertainty (possibly / perhaps / maybe), and lower probability (might / could). Once these are in active use, students can communicate accurately about events and ideas.
Build a certainty line on the board, marked from 0% to 100%. Place the words along it: definitely (100%), probably (80%), possibly (50%), might (30%), definitely not (0%). When students make a statement, ask: how sure are you? Then have them choose the word that matches that level. The visual scale and the question force precise word choice.
Choose the best certainty word for each situation. Think about how sure the speaker really is.
Each sentence has a problem with a certainty word — wrong level, wrong position, or wrong combination. Suggest a better version and explain.
Use this sequence directly in class — guided discovery, no textbook needed. Tap each step to mark it done.
STEP 1 — A scale from 100% to 0% (5 min): Draw a horizontal line on the board. Mark 100% on the left, 0% on the right. Place the words: definitely / probably / possibly / might / definitely not. Discuss each level. Establish that English has different words for different levels of confidence — and the right word matches the speaker's real confidence.
STEP 2 — Sure vs certain (5 min): Show the small differences. Both work after I am. Only certain works after it is. Drill: I am sure / I am certain (both correct), it is certain that (right) / it is sure that (wrong). Practise short sentences. Sure for everyday confident statements; certain slightly more formal.
STEP 3 — Probably vs possibly vs maybe (7 min): Show the middle of the scale. Probably (high — around 80%). Possibly (medium — around 50%). Maybe (medium — informal, position-restricted). Drill the position rule: maybe goes at the start; possibly can go anywhere; probably goes in the middle. Practise sentences in each pattern.
STEP 4 — Position rules (5 min): Write five sentences with the certainty adverb in the wrong position. Students fix them. The pattern is subject + auxiliary + certainty adverb + main verb: She will probably come, He has definitely arrived. Drill until automatic.
STEP 5 — How sure are you? (8 min): Ask students to make six statements about their own life or local situation, each at a different level of certainty. The exam will definitely take place next month. It will probably rain tomorrow. The new shop possibly opens next week. They might cancel the assembly. Share in pairs. Partner checks: did the certainty word match the actual confidence?
Use directly in class — copy, adapt, or read aloud. No printing needed.
For each strategy, choose the option that best describes where you are now.
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