Past Simple and Present Perfect
1. when... used in past simple这是具体的时间点
eg. -when did it start raining? -it started raining an hour ago.
how long...used in present perfect这是时间段
eg. -How long has it been raining? - It's been raining for an hour.
2. when we say a period of time we use for, but when we say the start of a period we use since
eg. I've been waiting for 2 hours; I've been waiting since 2 hours ago.
3. present perfect跟现在有关联，或者说告诉我们现在的情况。而past simple是过去的完成式行为
I have lost my key.指我过去丢失了钥匙，现在还没找到。而I lost my key.指过去丢失，但不知道现在有没有找到
4. present perfect还用于给出最新的信息，常用于新闻报道
Present Perfect Continuous and Simple
1. present perfect continuous用于刚刚结束或者还在进行
2.present perfect continuous表示我们关心的是活动本身；而simple关心的是活动的结果，即活动结束了
eg. My hands are very dirty. I have been repairing the car.
The car is Ok again now. I have repaired it.
Past Perfect Continuous
something had been happening for period of time before something else happened
eg. Ken gave up smoking 2 years ago. He had been smoking for 30 years.
but some verb( such as know and want) are not normally used in the continuous
eg. We were good friends. We had known each other for years.
Have and Have Got
We use have got or have for illnesses, pain etc
eg. I have got/ have a headache
but in the past we use had
eg. Ann had long fair hair, didn't she?
Used to (do)
It means that something happened regularly in the past but no longer happens, or something was true but is not true now.
eg. This building is now a furniture shop. It used to be a cinema.
It is past, if you want to talk about now, use the present simple
Present Tenses ( I am doing/ I do) for the Future
the present continuous to say what u have already arranged to do, more usual for personal arrangements. don't use will to talk about the arrangement
eg. What time are u meeting Ann tomorrow?
but present simple when we talk about timetables, programmes etc.
eg. The train leaves Hangzhou at 11.00 and arrives in Shaoxing at 11.15.
I am going to do means I have already decided to do it, or intended to do it(but perhaps not arranged to do it)
I was going to = I intended to do it but didn't do it
eg. I was just going to cross the road when somebody shouted " Stop".
Will do
用于说话者说话时所做的决定，或者是对未来的预测
shall用于询问will，但只用于I and we
will do和am going to do的区别在于，will do是说话当下做的决定，而am going to do是说话前就做好的决定
continuous进行时用于正在进行这个动作，包括过去、现在和未来
will be doing和will have done
will be doing是现在正在做，而will have done是在未来时这个动作已完成
Will you be-ing...?是询问某人的计划，尤其是你想要请求对方帮忙时
When I do/ When I have done When and If
When I do/ When I have done 的区别在于2个动作的前后顺序，一个可以同时也可以前后，另一个只能前后
eg. When I have phoned Kate, we can have dinner.
When I phone Kate this evening, I will invite her to the party.
if后面是一般现在时是用于表将来
eg. Hurry up! If we don't hurry, we will be late.
when和if 的区别是，when是确定发生，而if是可能发生
eg. When I go shopping, I will buy some fish.
If it is raining this afternoon, I won't go out.
Can, Could and (be) able to
can是这件事有可能发生，或者某人有能力做这件事
could是can的过去式，用于过去时态，但也可用于一般能力或者允许做某事。但当我们讲特殊的情况时，用was/were able to...
此外，could也可以用于讨论当下或未来可能发生的事，且其可能性比can还低
eg. I am so angry with him. I could kill him. (rather than I can kill him)
could have done是用于过去的事有可能发生，但没有发生
eg. The situation was bad but it could have been worse.
有时候，could means "would be able to...", could have done means "would have been able to"
eg. We could go away if we had enough money.
Must and Can't
must是用于we feel sure something is true
can't 用于we feel sure something is not impossible
对于过去时，用must have done and can't have done
May and Might
may or might 是用于现在，在未来是可能的行为。may/ might have done用于过去
may/might be-ing 是对未来可能的打算
might/ may as well= we should do something because there is nothing better to do and there is no reason not to do it
must and have to
must is personal. we use must when we give our personal feelings, but just for the present or future
have to is impersonal. we use have to for facts, not for our personal feelings, and used in all forms.
mustn't= it is necessary that you do not do it
don't have to = you don't need to do it( but you can if you want)