Now that（既然） you‘re studying English at a high level, you need to be able to talk about the language itself.
One of the biggest areas of confusion(混淆）for students is the difference between the past tense and the present perfect.
The past tense is indicated(表示） by use of the past tense marker, represented here by V sub d.
Here are some examples of regular verbs and their past tense forms.
So, as you can see, for regular verbs, the past tense form is indicated by the addition an- ed at the end of the verb.
However, some of the most common verbs in English are irregular, so it is important to learn them.
Here are some example.
All together there are over 200 irregular verbs.
Many people think that the past tense form only indicates the past time.
However, that is only one of the possible meanings.
The past tense form is also used to express something that is unlikely or imaginary, from the speaker's point of view.
Here is an example,:"He wishes he had a car."
The fact is that he doesn't have a car, so the use of "had" indicates that it isn't real:it's imaginary.
If he had a car, he could drive us to school.
Again he doesn't have a car, so he can't drive us to school.
This condition express something that isn't a fact.
It's a counter-factual (反事实的）condition, which means it goes against what we know or believe.
Look at these 2 sentences.
(If she waits another week, she can save money...
If she waited another week, she could save money because there's going to be a sale.)
Both sentences are correct. But there is a difference in meaning.
In the top sentence, the condition that she waits is more likely from the speaker's point of view.
In the bottom sentence, the speaker thinks it's less likely that she's going to wait.
