Using tenses correctly to describe some correct/incorrect events in the past

Question

Here are two examples:

I thought we had an exam.

I didn't know (that) you liked her.

The second example was taken from here. According to the discussions, it doesn't imply anything about the current status of the verb, like. The person might keep liking her or not. The first example describes the following situation: he was assuming that he was going to take an exam, but there was no exam.

Isn't there a contradiction? In the first example, past tense implies that the event doesn't exist but in the second one we cannot tell anything about the current status of 'like'?

I asked this because, I want to understand how I can say something like following:

2 days ago, I was thinking that the answer was 15 (I was wrong at that time but I did not know I was wrong). Then I did a bit research and now I believe the answer is 13. Can someone tell me which tenses I should use in order to express what I really meant.

Answer 1

When you use the past tense, you are saying that something was true in the past. It may or may not still be true in the present. The past tense of itself does not specify. There is no tense in English that means "was true in the past but is not true today", nor is there a tense that means "was true in the past and is still true today". Maybe there are other languages that have such tenses, but English does not.

If you want to make clear one way or the other, you have to use additional words. If you wanted to be very clear, you could spell it out. "Bob liked Sally then, but he does not like her any more." Or, "Bob liked Sally then, and he likes her just as much today."

If you put qualifiers on the time, it usually indicates that it is no longer true. Like, "Bob thought the neighbor's house was pretty before they painted it purple." The use of "before" implies that since they painted it purple, he no longer thinks it is pretty. But even as I type that example, it occurs to me that it could go either way depending on context. If I said, "Bob liked Sally before she won the lottery and became rich", that might mean that her personality changed after she became rich so that he doesn't like her any more, or it could mean that many people claim to like her now that she is rich, but Bob liked her before she was rich and still does, i.e. he doesn't just like her for her money.

Sometimes we want to be ambiguous. One reason is because you do not know the present status. Like suppose I say, "When I worked for XYZ Company 20 years ago, they had a big parking garage for the employees." At that time, they had the parking garage. Do they still have it today? Maybe I don't know.

I may want to be ambiguous to maintain suspense in a story. Like if I said, "The criminal escaped from prison and was free", I may very well not want to tell you at that point in the story whether he still is free or not. The whole point of the story may be to build suspense over whether he gets caught.