Class 19-3: Expressing Degrees of Certainty in the Past Tense

Degrees of certainty in the past tense means how confident we are that a specific topic was true or was not true – in the past. This means that the listener is understanding that the action you are discussing has already happened.

Rules:

If you are 100% sure about the topic you are discussing, use wasn’t or was not. You are 100% sure the topic was not correct.

Was not is used for a statement of fact.

Examples:

1. Tom wasn’t sad.

2. Tom wasn’t slow; he just won the race.

3. They were not at the theater when we arrived.

If you are 90% sure about the topic you are discussing, use couldn’t have been or could not have been. You believe the possibility of the topic being true is very small.

1. Seth couldn’t have been blind; he just read a magazine.

2. Seth couldn’t have been starving; he just ate lunch.

If you are 80% sure about the topic you are discussing, use must not have been. Similar to couldn’t have been, you have no evidence to support your opinion. This is a strong belief.

The difference between must not have been and couldn’t have been is that you are more sure when using must not have been. (Examples 6 and 7)

Sarah wasn’t at school yesterday, she must not have been well.

Answer: No, Tom was at soccer practice last week, so he must not have been injured.

If you are 60% sure about the topic you are discussing, use may not have been or might not have been. You are discussing suspicious or uncertain thoughts about the topic.

Statement: I don’t think Sophia was sick.

Rules:

If you are 100% sure about the topic in the past, use was. You are 100% sure the topic was correct.

Examples:

1. Tom was happy.

2. Tom was slow, then he practiced, and became fast.

If you are 90% sure about the topic you are discussing, use must have been. You believe in the small possibility that the topic is true.

1. Sarah wasn’t at school yesterday; she must have been  sleeping.

2. The dog must have been hungry; he ate the trash.

If you are 80% sure about the topic you are discussing, use could’ve been or could have been.

The difference between must have been and could have been is that you are more sure when using must have be.

1. I don’t know if she was sick, but she could’ve been.

2. I don’t know if she’s still at the party. She could’ve left early.

If you are 60% sure about the topic you are discussing, use may have been or might have been.

*Note: even though your thoughts are in the present, the action still happened in the past.

1. Susan went home early. She may have been sick.

2. The dog went through the trash. He might have been hungry.