as if与even if、 even though的异同在哪里？

as if好像
as though好像，仿佛
even if即使
even though尽管
他们两两间在含义上并无太大区别，一般情况下可以通用；

【though 常表示一些已经确定的消息，而if由它本身所带的“如果”的含义，表示了一种对假设信息的不确定】

as though 与 as if 相比而言，as if 更强调if，而as though更强调though，一个更突出条件，一个更突出转折，如，
1、在as if从句中表达与现在事实相反从句用过去时
He felt as if he alone were responsible for what had happened .
他感到仿佛他要独自为所发生的一切负责。
2、在as though从句中,表示过去想象中的动作或情况，从句用过去完成时。
The machine operated as though it had been repaired .
这台机器运行起来好像已被修理过似的

even though 和even if 相比，even if一般引导的是把握不大或假设的事情, 而even though引出的是事实。如，
1、She's going to have problems finding a job even if her gets she A levels. 就算她考试成绩都是A，她找工作还会碰到问题。（考A是假设的情况）
2、Even though he's 24 now, he's still like a little child.尽管他24岁了，但他仍然像个孩子。（他24岁了是事实）

3、再对比一下仔细体会
Even though he knows it, he'll not let out the secret.（他知道这个秘密）.
Even if he knows it, he'll not let out the secret.（不确定他是否知道这个秘密）.

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