Past Deductions with Must, Might, and Cannot Have

What you’ll learn

Evaluate explanations for past events.

វាយតម្លៃការពន្យល់អំពីហេតុការណ៍អតីតកាល។

Meaning and use

Modal + have + past participle places a judgment about an event in the past. Must have gives a strong positive deduction; cannot or could not have gives a strong negative deduction; may, might, or could have gives possibility. Could have can also describe an unused opportunity, so context is essential.

Modal + have + past participle ប្រើសន្និដ្ឋានអតីតកាល។ Must have សន្និដ្ឋានមុតមាំ; might have បង្ហាញលទ្ធភាព; cannot have បដិសេធតាមភស្តុតាង។

Grammar patterns

Pattern	Example or form
Past positive / possible	must have left / might have left
Past negative deduction	cannot/could not have left

Examples

1. She must have missed the train; she is still at the station.

   នាងទំនងជាខករថភ្លើង ព្រោះនាងនៅស្ថានីយនៅឡើយ។

2. He might have sent it to the wrong address.

   គាត់ប្រហែលជាបានផ្ញើទៅអាសយដ្ឋានខុស។

3. Dara cannot have taken it; he was abroad.

   ដារ៉ាមិនអាចជាអ្នកយកវាទេ ព្រោះគាត់នៅបរទេស។

4. They could have misunderstood the instructions.

   ពួកគេប្រហែលជាយល់ការណែនាំខុស។

Everyday conversation

Dara: Why did nobody reply?

Maly: They might have gone home already, or the message may have failed.

Common mistakes

Instead of	Use	Why
She must have went home.	She must have gone home.	A perfect modal uses a past participle.
He might had forgotten.	He might have forgotten.	The verb after a modal remains the base have.

Practice

Try these questions before opening the answers. Write or say each answer.

សាកល្បងឆ្លើយសំណួរទាំងនេះជាមុនសិន មុននឹងបើកមើលចម្លើយ។ អ្នកអាចសរសេរ ឬនិយាយចម្លើយរបស់អ្នក។

1. Complete a strong deduction: The ground is wet. It ___ rained overnight.
2. Complete: They might have ___ (take) the earlier bus.
3. Does She might have called state that she definitely called?

Answers and explanations

Show answers / បង្ហាញចម្លើយ

1. must have

   The evidence supports a strong past conclusion.

2. taken

   Use the past participle taken.

3. No.

   It presents a possible past event, not a confirmed fact.

Quick recap

• Past positive / possible: must have left / might have left
• Past negative deduction: cannot/could not have left