Module 4: Mastering Modal Verbs - Lesson 4.11: Modal Verbs of Deduction (Possibility & Impossibility): MAY, MIGHT, COULD, CAN'T

Lesson 4.11: Modal Verbs of Deduction (Possibility & Impossibility) - MAY, MIGHT, COULD, CAN'T

In this lesson, we will expand our exploration of modal verbs for deduction to include MAY, MIGHT, COULD, and CAN'T. These modals, along with MUST (from the previous lesson), allow us to express varying degrees of certainty and possibility when making logical conclusions based on evidence or reasoning. While MUST expresses strong certainty, MAY, MIGHT, COULD, and CAN'T are used to express possibility, weaker certainty, and impossibility in deductions.

Modal Verbs for Deduction: Expressing Different Levels of Certainty

We use a range of modal verbs to express our degree of certainty when making deductions. These modals fall on a spectrum of certainty:

MUST (Deduction): Expresses strong certainty that something is true. (Covered in Lesson 4.10)
MAY, MIGHT, COULD (Deduction): Express possibility or likelihood that something is true. They indicate that something is *possibly* the case, but we are not completely sure.
CAN'T (Deduction): Expresses strong certainty that something is *not* true - impossibility.

This lesson will focus on MAY, MIGHT, COULD for possibility in deductions, and CAN'T for impossibility in deductions.

MAY, MIGHT, COULD (Deduction) - Expressing Possibility and Likelihood

MAY, MIGHT, and COULD are all used to express possibility or likelihood when making deductions. They indicate that something is possibly true based on the available evidence, but there is still a degree of uncertainty. These modals are often interchangeable in many contexts for deduction about possibility.

Key Uses of MAY, MIGHT, COULD (Deduction - Possibility):

Expressing Possibility in Deductions: To indicate that something is possibly true, based on the available evidence or reasoning. You are not certain, but it's a plausible explanation.
Speculation and Tentative Conclusions: Used when you are speculating or making a tentative conclusion, acknowledging that other possibilities exist.
Weaker Deductions Than "MUST": These modals express less certainty than "must." They suggest a range of possibilities rather than a single, highly probable conclusion.

Forming Sentences with MAY, MIGHT, COULD (Deduction - Possibility):

The structure is the same for all three modals:

Formula: Subject + may / might / could + Base Verb (Often uses the verb "be" or "have" as the base verb for states and situations)

Examples of MAY, MIGHT, COULD (Deduction - Possibility) in Use:

Expressing Possibility in Deductions:
- "He may be late. His train is often delayed." / "He might be late." / "He could be late." (Possibility of lateness - based on knowledge of train delays) - Interchangeable modals here.
- "She may not know about the meeting. She's new in the team." / "She might not know." / "She could not know." (Possibility of lack of knowledge - based on her being new) - Interchangeable modals for negative possibility.
- "That may be the answer." / "That might be the answer." / "That could be the answer." (Suggesting a possible solution - tentative suggestion) - Interchangeable modals for tentative suggestions.
- "They may have gone home already." / "They might have gone home." / "They could have gone home." (Possibility about a past action - speculating about their whereabouts) - Using "may/might/could have + past participle" for past deductions of possibility.
Speculation and Tentative Conclusions:
- "Who is that man? It may be her brother." / "It might be her brother." / "It could be her brother." (Speculating about someone's identity - acknowledging uncertainty) - Interchangeable modals for speculation.
- "Where's my wallet? I may have left it at home." / "I might have left it at home." / "I could have left it at home." (Speculating about a lost item - considering possible locations) - Using "may/might/could have + past participle" for past speculative deductions.
- "Why is the traffic so bad? There may be an accident." / "There might be an accident." / "There could be an accident." (Tentative conclusion based on observation - possible cause of traffic) - Interchangeable modals for tentative conclusions.

CAN'T (Deduction) - Expressing Impossibility and Strong Negative Deduction

CAN'T (or CANNOT) is used to express impossibility or strong negative deduction. It indicates that you are almost certain that something is not true based on logic and evidence. It is the negative counterpart to MUST (deduction).

Key Uses of CAN'T (Deduction - Impossibility):

Expressing Strong Negative Deduction and Impossibility: To indicate that you are almost certain something is *not* true in the present moment, based on logical reasoning or strong evidence.
Logical Conclusion that Something is False: Used when you can logically conclude with high confidence that something is false or impossible given the available clues.
Opposite of MUST (Deduction): "Can't" (deduction) is the direct opposite of "must" (deduction). "Must" says you are sure it *is* true; "can't" says you are sure it is *not* true.

Forming Sentences with CAN'T (Deduction - Impossibility):

The structure is:

Formula: Subject + can't / cannot + Base Verb (Often uses the verb "be" or "have" as the base verb for states and situations)

Examples of CAN'T (Deduction - Impossibility) in Use:

Expressing Strong Negative Deduction and Impossibility:
- "That can't be right. Two plus two is four, not five." (Strong negative deduction - logically impossible based on math)
- "She can't be serious! She's joking, surely." (Strong disbelief - impossible to believe something is serious)
- "He can't be at work today. It's Sunday." (Strong negative deduction - impossible to be at work on a day off)
- "They can't have finished the project already. It only started this morning." (Strong negative deduction about a past action - impossible to complete so quickly) - Using "can't have + past participle" for past negative deductions.
- "This can't be my key. Mine is silver, and this one is gold." (Strong negative deduction based on visual evidence - key mismatch)
Logical Conclusion that Something is False:
- "[Someone attempts to open a locked door] It can't be open. I locked it myself." (Logical impossibility - speaker knows it's locked)
- "He says he's 120 years old. That can't be true! Nobody lives that long." (Logical impossibility based on general knowledge - life expectancy)
- "She can't have seen me. I was wearing sunglasses and a hat." (Logical impossibility of being seen - disguised appearance) - Using "can't have + past participle" for past negative deductions.
- "They can't be enjoying the party. They left after only 10 minutes and looked unhappy." (Logical impossibility of enjoyment - based on observed behavior) - Using "can't be + -ing form" for deduction about current state/action.

MAY, MIGHT, COULD, CAN'T (Deduction): Key Differences - Degrees of Certainty

MUST (Deduction): Strong certainty (positive). Almost sure it is true.
MAY, MIGHT, COULD (Deduction): Possibility/Likelihood (neutral certainty). Possible it is true, but not certain. Often interchangeable.
CAN'T (Deduction): Strong certainty (negative). Almost sure it is *not* true - impossible.

These modal verbs provide a spectrum for expressing your confidence level when making deductions. "Must" and "Can't" represent the highest levels of certainty (positive and negative respectively), while "may," "might," and "could" indicate varying degrees of possibility and speculation in between. Understanding and using this range allows you to communicate your deductions with precision, reflecting your actual level of confidence in your conclusions.

Key takeaway: MAY, MIGHT, and COULD express possibility in deductions - that something is possibly true based on evidence. CAN'T expresses impossibility in deductions - that something is almost certainly *not* true. These modals, along with MUST, allow you to express a range of certainty when making logical conclusions. Next, we will explore Modal Verb of Advice/Suggestions: HAD BETTER!