Making deductions: expressing certainty and uncertainty
1
Think about these questions before reading. Share your ideas with a partner.
- When you meet someone for the first time, what clues do you use to form an impression of their personality or job? How often do you think your initial deductions are correct?
- Describe a time you had to solve a small mystery or figure out a confusing situation with limited information. What steps did you take to deduce what was happening?
- In what kind of professional or academic situations is it important to express uncertainty rather than absolute confidence? Why might this be a useful communication skill?
2
Deducing a Tech Problem
Listen to the dialogue. Notice how the vocabulary and grammar from the lesson are used.
3
Answer these questions in your own words based on your understanding of the article.
01According to the article, what is the main purpose of using modals of deduction?
Sample answerTheir main purpose is to express how certain or uncertain we are about something. It's about showing our level of confidence when we are guessing or concluding something.
02In what kinds of real-life situations does the article suggest it is particularly important to express levels of certainty?
Sample answerThe article mentions two main contexts: in normal, everyday conversations and also in more formal professional discussions, like at work.
03How does the article differentiate between the level of certainty expressed by 'must' versus 'might' or 'could'?
Sample answerIt explains that 'must' shows strong certainty, meaning you feel something is almost definitely true. In contrast, 'might' or 'could' express uncertainty, indicating something is just a possibility, not a strong conclusion.
04Based on the text, what is the likely connection between vocabulary like 'evidence' or 'clue' and the act of making a deduction?
Sample answerThe connection is that evidence and clues are the pieces of information you use to make a deduction. The strength of your evidence would likely determine which modal you choose, for example, strong evidence might lead you to use 'must'.
4
Grammar: Modals of deduction in the present and past
Grammar
Modals of deduction (must, can't, might, may, could) express how certain we are about something based on evidence. We use them with a base verb to speculate about the present, and with 'have + past participle' to make deductions about the past. This is essential for logically inferring information that isn't explicitly stated.
Examples
Her phone is going straight to voicemail. She must be on the plane already.
Use 'must + infinitive' when you are almost 100% certain that something is true in the present based on strong evidence.
The report isn't in my inbox. He might have forgotten to send it, or perhaps the email is just delayed.
Use 'might/may/could + have + past participle' to express a possibility in the past. These modals show you are uncertain.
She can't have finished the entire project by herself in one day; it was far too complex.
Use 'can't have + past participle' for strong certainty that something was impossible or did not happen in the past. We do not use 'mustn't have' for this.
Key points
- Use 'must' for strong positive certainty and 'can't' for strong negative certainty.
- For past deductions, the structure is 'modal + have + past participle'.
- Common mistake: Don't use 'mustn't' for deduction. 'Mustn't' expresses prohibition, while 'can't' expresses impossibility.
5
Correct the sentences
Read the sentences below, which are all related to making deductions. Each one has a single mistake.
Find the one error in each sentence and correct it.
01The package arrived this morning, so it must to have been sent yesterday.
Corrected version
The package arrived this morning, so it must to have been sent yesterday.
02He looks exhausted. He can't have sleep well last night.
Corrected version
He looks exhausted. He can't have sleep slept well last night.
03Based on the wet roads, I can deduce that it might had rained earlier.
Corrected version
Based on the wet roads, I can deduce that it might had have rained earlier.
04There isn't enough evidense to be certain about what happened.
Corrected version
There isn't enough evidense evidence to be certain about what happened.
05I'm not sure what this word means; I should speculate it's a technical term.
Corrected version
I'm not sure what this word means; I should speculate it's a technical term.
06From his angry expression, I implied that he disagreed with the plan.
Corrected version
From his angry expression, I implied inferred that he disagreed with the plan.
07She isn't answering her phone. She could be drove and unable to pick up.
Corrected version
She isn't answering her phone. She could be drove driving and unable to pick up.
6
Key vocabulary for making deductions
Vocabulary
These expressions will help you communicate more naturally when discussing certainty and uncertainty.
Examples
A gut feeling — an intuition or instinct you have about a situation, not based on facts or evidence.
Usage note: This is an informal expression. You can say 'I have a gut feeling that...' or 'My gut feeling is...' to express a strong personal belief without proof.
To jump to conclusions — to make a decision or form an opinion about something too quickly, without knowing all the facts.
Usage note: This phrase has a negative meaning, suggesting a mistake in reasoning. It's often used as a warning: 'Let's not jump to conclusions before we see the report.'
On the balance of evidence — a phrase used to say that something is the most likely conclusion after considering all the available information.
Usage note: This is a more formal phrase, suitable for discussions or writing. It shows you have thought carefully about your deduction. For example: 'On the balance of evidence, it must be the correct answer.'
To read between the lines — to understand someone's real feelings or intentions from what they say or write, even if it is not explicitly stated.
Usage note: This describes a type of social deduction. For example: 'He said he was happy with the decision, but reading between the lines, I think he was disappointed.'
A safe bet — something that is very likely to be true, to happen, or to be successful.
Usage note: This is a common, informal way to express strong certainty. You can say 'It's a safe bet that...' For example: 'It's a safe bet that it will rain tomorrow if you see those clouds.'
7
Complete the sentences with words from the box. One word is extra.
Word bank
01I can't explain it logically, but I have a strong gut that something isn't right with his story.
02Let's not jump to until we've heard both sides of the argument and seen all the facts.
03On the balance of , the detective concluded that the butler was the most likely suspect.
04She didn't say she was unhappy, but if you read between the , you could tell she was disappointed.
05Given her excellent qualifications and experience, it's a safe that she'll get the job.
8
Choose the best answer based on the article.
01According to the article, how will students apply the lesson's language in a practical, interactive way?
02The article highlights several key verbs. Which verb best describes the act of guessing or forming a theory about something without having firm evidence?
03What is a specific feature of the vocabulary expansion section mentioned in the article?
04The lesson plan described in the article includes various stages. Which of the following is NOT mentioned as a component of the lesson?
9
Discuss these questions with a partner. Try to use vocabulary from the lesson.
- When making a significant life decision, like choosing a career or a partner, is it more reliable to trust 'a gut feeling' or to decide 'on the balance of evidence'? Which approach do you think leads to better outcomes?
- In your culture, how important is it to 'read between the lines' in everyday conversations? Do you think this leads to more accurate deductions about people's intentions, or does it sometimes cause people to 'jump to conclusions' unfairly?
- Imagine a new colleague joins your team. They are very quiet and rarely share personal information. What would be 'a safe bet' to deduce about their personality, and what would be 'jumping to conclusions'? How can you avoid making incorrect deductions in such professional situations?