if条件句虚拟语气不同时态的辨析(if had used, if could have used)

书上原句：（海明威老人与海）

a) If I could have used a bat with two hands, I could have killed the first one surely. （虚拟语气）

如果我可以用双手抡起一根棒球棒，我准能把第一条鲨鱼打死。



我疑惑的是为何原句a)中if条件句用了could have used ? 怎么样理解？



假如把could have used改成had used,如下b)句：

b) If I had used a bat with two hands, I could have killed the first one surely.



意思有变化吗？



a) If I could have used a bat with two hands, I could have killed the first one surely.

b) If I had used a bat with two hands, I could have killed the first one surely.

两句都对，意思略有差别。

第一句比第二句，多了一层意思“可以”。could 表示“能力”。

哪个告诉过你，if 从句不可以用 could？用might 也可以。

if 从句中，had used 和 could have used 分别表示“过去未做到” 和 “过去未能做到”。后者比前者多了一个“可以”。其他都一样。

我再用 could 举一个例子：

If he could come, we would not go out.

假如他可能来的话，大家就不走了。

意思是：他来的可能性极小。这是与“以后” 不符的虚拟语气。

以下说法，都可以：

If he came, we would not go out.

If he could come, we would not go out.

If he might come, we would not go out.

If he should come, we would not go out.

If he were to come, we would not go out.