SECOND CONDITIONAL
UNREAL POSSIBILITY OR DREAM
the second conditional is like the first conditional. we are still thinking about the future. we are thinking about a particular condition in the future, and the result of this condition. but there is not a real possibility that this condition will happen. for example, you do not have a lottery ticket. is it possible to win?no¡ lottery ticket, no win¡ but maybe you will buy a lottery ticket in the future. so you can think about winning in the future, like a dream. it's not very real, but it's still possible.


IF   CONDITION               RESULT
       past simple              WOULD + base verb
If    I won the lottery       I would buy a car  


notice that we are thinking about a future condition. we use the past simple tense to talk about the future condition. we use WOULD + base verb to talk about the future result. the important thing about the second conditional is that there is an unreal possibility that the condition will happen.


EXAMPLES. 
IF + SIMPLE PAST + SIMPLE CONDITIONAL


-If I were rich, I would buy a castle
-If I were him, I would go and see a doctor
-If elephants had wings, they would be able to fly 



THIRD CONDITIONAL: Imaginary past
The third conditional is used when we are talking about the past and imagining something different from what actually happened:

     CONDITION              RESULT                      WHAT ACTUALLY HAPPENED 
      past perfect      would have + past participle    
IF  I had known        I would have helped              I didn't know and didn't help 

IF  CONDITION                 RESULT                           CERTINTY   
-      past perfect       would have + past participle     
-IF  I had known       I would have helped                  although this didn't happen, the speaker is sure 
                                                                                    about the result
-IF I had known       I could have helped                    although this didn't happen, the result is only a 
                                                                                    possibility
-IF I had known      I might have helped                    although this didn't happen, the result is only a  
                                                                                   possibility
-IF you had known   you should have helped            although this didn't happen, it is only a good 
                                                                                   suggestion or piece of advice

EXAMPLES:  
-If I had known that you were sick, I would have gone to see you 
-If you had saved your  money, you could have bought a laptop
-If you hadn't been late for work so often, they wouldn't have fired you