1. Lesson Overview
In this lesson, you will learn how modal verbs express different levels of certainty and probability.
Modal verbs such as must, may, might, and could allow speakers to express logical conclusions, predictions, and uncertainty.
Instead of stating something as an absolute fact, modal verbs allow speakers to indicate how certain they are about a situation.
Example:
The lights are off. The researchers must be working in another laboratory.
(strong logical deduction)
The results may change after further analysis.
(possibility)
Understanding these distinctions allows learners to express subtle differences in probability and certainty.
By the end of this lesson, you will be able to:
-
explain how modal verbs express degrees of certainty
-
use must for strong logical deduction
-
use may, might, and could to express possibility
-
recognise modal verbs used in predictions and logical conclusions
2. Concept Introduction
Consider the following sentences:
The laboratory door is locked. The technician must be inside.
The technician may be inside.
The technician might be inside.
Each sentence expresses a different level of certainty.
| Modal | Degree of Certainty |
|---|---|
| must | very strong probability |
| may | possible |
| might | less certain |
| could | possible |
These modal verbs help speakers express logical judgement rather than factual statements.
3. Core Explanation
Modal verbs expressing probability allow speakers to indicate how certain they are about an event or situation.
Must – Strong Logical Deduction
Must is used when the speaker believes something is almost certainly true based on evidence.
Example:
The lights are still on. The researchers must be working late.
This expresses a strong logical conclusion.
May – Reasonable Possibility
May indicates that something is possible but not certain.
Example:
The results may change after further testing.
Might – Weaker Possibility
Might expresses a lower degree of certainty.
Example:
The results might change after further testing.
Could – General Possibility
Could expresses a potential outcome or possibility.
Example:
The new method could improve the results.
4. Rule Table
Modal Verbs Expressing Certainty
| Modal | Meaning | Example |
|---|---|---|
| must | strong logical deduction | The results must be correct. |
| may | possible | The results may change. |
| might | weaker possibility | The results might change. |
| could | general possibility | The results could improve. |
Structure for Probability
| Structure | Example |
|---|---|
| subject + modal + base verb | The results may change. |
| subject + modal + be + complement | The technician must be inside. |
5. Usage
1. Logical deduction
Example:
The equipment is warm. The system must have been running recently.
2. Expressing possibility
Example:
The results may change after further testing.
3. Expressing weaker probability
Example:
The results might improve with additional data.
4. Predicting potential outcomes
Example:
The new software could increase efficiency.
5. Expressing cautious conclusions in research
Example:
The results may indicate a relationship between the variables.
This cautious style is common in academic writing.
6. Signal Words
Certain expressions often accompany modal verbs expressing probability.
| Expression | Example |
|---|---|
| perhaps | The results may improve. |
| possibly | The system could fail under pressure. |
| it is likely that | The system must be functioning correctly. |
| there is a chance that | The results might change later. |
| it is possible that | The experiment could succeed. |
These expressions reinforce the idea of uncertainty or probability.
7. Special Cases
Modal + Be + Present Participle
Modal verbs can express probability about ongoing actions.
Example:
The researchers must be analysing the results now.
Modal + Have + Past Participle
This structure expresses probability about past events.
Example:
The technician may have forgotten to restart the system.
Example:
The team must have completed the experiment earlier.
8. Additional Notes
Modal verbs expressing probability are especially important in scientific and academic writing, where absolute certainty is often avoided.
Example:
The data may suggest a correlation between the variables.
Such expressions allow researchers to present conclusions carefully and objectively.
9. Common Errors
⚠ Using must for obligation instead of deduction
Incorrect:
The lights are on. The researchers must follow the procedure.
Correct:
The lights are on. The researchers must be working.
Explanation:
Use must to express logical deduction, not obligation in this context.
⚠ Adding “to” after modal verbs
Incorrect:
The results may to change.
Correct:
The results may change.
Explanation:
Modal verbs are followed by the base verb.
⚠ Using modal with incorrect verb form
Incorrect:
The results might changes.
Correct:
The results might change.
Explanation:
Verbs following modals must remain base form.
⚠ Confusing levels of certainty
Incorrect:
The results must change tomorrow.
(if expressing uncertainty)
Correct:
The results may change tomorrow.
Explanation:
Use may/might/could for possibility.
⚠ Incorrect modal structure for past probability
Incorrect:
The technician may forgot the instructions.
Correct:
The technician may have forgotten the instructions.
Explanation:
Past probability requires modal + have + past participle.
10. Lesson Mastery
After completing this lesson, you should now be able to:
✅ explain how modal verbs express degrees of certainty and probability
✅ use must for strong logical deduction
✅ use may, might, and could to express possibility
✅ apply modal verbs to express predictions and logical conclusions