牛津实用英语语法:312 could用于间接引语
A could表示能力
1 could表示目前的能力时在间接引语中保持不变：
I cant/couldnt stand on my head，he said.
他说：我不能做三点倒立。相当于：
He said he couldnt stand on his head.
他说他不能做三点倒立。
2 could表示将来的能力时，在间接引语中可以保持不变，或由would be able结构来转述：
He said，I could do it tomorrow.
他说：我明天能做这事。相当于：
He said he could do it/would be able to do it the next day.
他说他第二天能做这事。
3 条件句类型2中，主句中的could与A2中的变化相同：
If I had the tools I could mend it，he said.
他说：如果我有工具的话，我就能修补它。相当于：
He said that if he had the tools he could/would be able to mend it.
他说如果他有工具的话，他就能修补它。
would be able在这里暗指所假设的情况有可能实现(可能他可以借到工具。)
4 条件句类型3中，could被转述时保持不变。
5 could表示过去的能力时，在间接引语里保持不变，或用had been able结构转述：
I could read when I was three!she boasted.
她吹嘘说：我三岁时就能看书了!相当于：
She boasted that she could/had been able to read when she was three.
她吹嘘说她三岁时就能看书了。
B could表示允许
1 条件句类型2中的could在间接引语中可保持不变，或由would be allowed to转述：
If I paid my fine I could walk out of prison today，he said.
他说：如果我交了罚款，我今天就能走出牢门了。相当于：
He said that if he paid his fine he could/would be allowed to walk
他说如果他交了罚款他会被允许走
2 表示过去时态的could在间接引语中可保持不变，或用 was/were allowed to或had been allowed to结构来转述：
He said，When I was a boy I could stay up as long as I liked.
他说：我小时候，我可以想呆到多晚睡觉就呆到多晚。相当于：
He said that when he was a boy he could/was allowed to stay up./He said that as a boy he was/had been allowed etc.
他说他小时候，可以/被允许爱呆到多晚睡觉就呆到多晚。
A could表示能力
1 could表示目前的能力时在间接引语中保持不变：
I cant/couldnt stand on my head，he said.
他说：我不能做三点倒立。相当于：
He said he couldnt stand on his head.
他说他不能做三点倒立。
2 could表示将来的能力时，在间接引语中可以保持不变，或由would be able结构来转述：
He said，I could do it tomorrow.
他说：我明天能做这事。相当于：
He said he could do it/would be able to do it the next day.
他说他第二天能做这事。
3 条件句类型2中，主句中的could与A2中的变化相同：
If I had the tools I could mend it，he said.
他说：如果我有工具的话，我就能修补它。相当于：
He said that if he had the tools he could/would be able to mend it.
他说如果他有工具的话，他就能修补它。
would be able在这里暗指所假设的情况有可能实现(可能他可以借到工具。)
4 条件句类型3中，could被转述时保持不变。
5 could表示过去的能力时，在间接引语里保持不变，或用had been able结构转述：
I could read when I was three!she boasted.
她吹嘘说：我三岁时就能看书了!相当于：
She boasted that she could/had been able to read when she was three.
她吹嘘说她三岁时就能看书了。
B could表示允许
1 条件句类型2中的could在间接引语中可保持不变，或由would be allowed to转述：
If I paid my fine I could walk out of prison today，he said.
他说：如果我交了罚款，我今天就能走出牢门了。相当于：
He said that if he paid his fine he could/would be allowed to walk
他说如果他交了罚款他会被允许走
2 表示过去时态的could在间接引语中可保持不变，或用 was/were allowed to或had been allowed to结构来转述：
He said，When I was a boy I could stay up as long as I liked.
他说：我小时候，我可以想呆到多晚睡觉就呆到多晚。相当于：
He said that when he was a boy he could/was allowed to stay up./He said that as a boy he was/had been allowed etc.
他说他小时候，可以/被允许爱呆到多晚睡觉就呆到多晚。
