鉴别虚拟语气主要看的是时态.
与现在事实相反,从句用一般过去时,其中be动词统一用were,主句用would或was/were going to加动词原形,也就是过去将来时.比如,if I were you, i would not agree with it.
与过去事实相反,从句用过去完成时,主句用would或was/were going to加完成时,也就是过去将来完成时.比如,if he had accepted my advice, he would not have failed the exam.
与将来事实相反时,条件从句的时态为一般过去时/（were+不定式）/（should+动词原形）,比如,if you succeeded, I would give you a surprise.
与现在事实相反和将来事实相反的时态是很相近的,要看意思.
if...will...是条件状语从句,是可能发生,if后面用现在时态表示将来.