虚拟语气中的should would可以无条件换用吗?

1 Like the rules governing the use of shall and will on which they are based, the traditional rules governing the use of should and would are largely ignored in modern American practice. Either should or would can now be used in the first person to express conditional futurity:
就象作为shall 和 will 词的基础的限用的用法规则一样， 适用于should 和 would 这个词的传统使用规则在现代美国英语中也已被忽略了。 现在should 或 would 这两个词中的任何一个都可以用于第一人称，表示条件式中的将来：
If I had known that, I would (or somewhat more formally, should ) have answered differently.
如果已经知道了这个情况的话，我就（或正规一点用 should ） 不会那么回答了 ，
2 But in the second and third persons only would is used:
但在第二人称或第三人称中只用would ：
If he had known that, he would (not should ) have answered differently.
如果他知道那个情况的话，就（不能用 should ） 不会那么回答了。
3 Wouldcannot always be substituted for should, however. Should is used in all three persons in a conditional clause:
但是Would并不是总是能由 should 代替。 Should 在三种人称的条件从句中都可以用：
if I (or yo