句子中had I 是什么用法，高中虚拟语气省略倒装的语法点。
当虚拟条件句的谓语动词含有were,should,had时,if可以省略,这时条件从句要用倒装语序,即把were,should,had等词置于句首,这种多用于书面语。
完整原句：Looking back, I feel I wouldn't be able to ride a bike if I had lost heart。如果是一个简单的从句一般来说是提前置于句首的。Had I lost heart,I wouldn't be able to ride a bike。
虽然知道是用来考虚拟语气，但句中倒装还要套一个I feel，越看越别扭，没事不要学，老实用If连接。
Looking back, I feel (I wouldn't be able to ride a bike if I had lost heart)正常是句首倒装Had I lost heart, I wouldn't be able to ride a bike = If I had lost heart。
Looking back, I feel I wouldn’t be able to ride a bike had I lost heart. 首先这句话是一句虚拟语气，所谓虚拟语气，就是只存在于说话人的脑袋里，而不存在于真实世界中。
这句话首先是虚拟语气叠加倒装句，因此第一看上去会很懵，那么咱们来还原下句子： Looking back, I feel I wouldn’t be able to ride a bike if I had lost heart. 这句话显然：要不是我过去失去信心，我就不能学会骑自行车。
你肯定是会骑自行车的，而且 “学会骑自行车”是过去的事， “那失去信心”是 “ 学会骑自行车” 之前的事，因此， “if I had lost heart” 这个条件是过去完成时， “ I wouldn’t be able to ride a bike” 是过去将来时。
