When we talk about something that happened in the past, we use the past tense. However, there are also times when we use the past tense to express something else.

a). To express a wish    
A wish is not something that happened in the past, but we need to use the past tense.
e.g.
I wish I had a car. (I do not have a car.)
He wishes he won the lottery.

In the above sentences, the past tense has nothing to do with the past time.

b). In the sentence pattern “It’s time …”
When “It’s time” followed by a clause, the past tense is used in the clause.

e.g.
It’s time we left.
It’s time we took design seriously.
It’s time you sold your old car.

Here we are not talking about what happened in the past. If I say “It’s time you sold your old car.” to you, you still have your car, and you are driving it.

c). To show politeness 
Sometimes we use the past tense because we want to be polite. The past tense is more polite than the present tense.

e.g.
I wonder if you can come to dinner tonight.
I wondered if you could come to dinner tonight.
I was wondering if you could come to dinner tonight.

If you are inviting a friend, you use the first sentence. If you are inviting your boss, you probably will use the second or the third sentence. The third, the past progressive tense, is even more polite than the second.

d) In the “if” clause 

We use the past tense in the “if” clause, if something is not a fact, or it’s unlikely to happen.

e.g.
If it rained tomorrow, I would not come. (I think it will rain tomorrow.)
If I got a raise, I would throw a party. (I don’t believe I will get a raise.)

When we use the simple present tense, it means that we believe it will happen.

e.g.
If it rains tomorrow, I will not come. (I don’t think it will rain tomorrow.)
If I get a raise, I will throw a party. (I think I will get a raise.)

Generally speaking, the past tense is used to express the past time, but there are special uses of the past tense. We need to pay attention to these special uses in learning English.

- Ron Lee -