想象自己是一只鸟,理解虚拟语气基本用法

印度诗人泰戈尔《飞鸟集》(Stray Birds)中有这样的诗句:The cloud wishes it were a bird,the bird wishes it were a cloud.云儿愿为一只鸟,鸟儿愿为一朵云。