Conditional Sentence

If 嘅sentence 叫 conditional sentence, 分左 4 種 

Type 0. 當講緊事實
If (present tense), (present tense) 

If I mix yellow with blue, it turns green.

Type 1. 當係講緊一件好有可能發生嘅事
If (present tense), will + infinitive

If it rains tomorrow, I will cancel the picnic. 

Type 2. 當件事係好細機會發生/冇可能
If (past tense), would + infinitive 

If I were you, I would break up with him.

Type 3. 講緊過去/你後悔嘅事
If (past perfect tense), would have + past participle 

If I had not killed a man, I would have been free now.

當講一啲冇可能發生嘅野,  就一定要用type 2, 所以If I were you依啲幻想/假設性質就一定要用past tense.