一、意义上的区别
look 指视觉印象，appear 指外表给人的印象，这两者可能是真象也可能是假象，appear的不确定性更大一些，seem 侧重指根据某种迹象作出的推断，也不一定是事实。
二、后接不定式的问题
三者均可后接不定式，但 look 之后一般只限于 to be(且较少见)：
He seems [appears, looks] to be very tired. 他好像很累了。
He seems [appears] to have traveled a lot. 他似乎去过不少地方。
但是不说He looks to have traveled a lot.
三、后接介词like的问题
look, seem 之后可接介词 like，但 appear 之后一般不能：
He looks [seems] like a fool. 他看起来像个傻瓜。
四、用于进行时态的问题
appear 和seem不用于进行时态，但look有时可这样用(尽管较少见)：
He looks [is looking] well. 他看上去气色不错。
但是不说He is seeming [appearing] well.
五、用于it开头的句子
三者均可用于 it 开头的句子，且三者之后均可接以 as if 或 as though 引导的从句，另外 appear 和 seem 之后还可接 that 引导的从句：
It looks [seems, appears] as if he has lost interest in his job. 看来他对自己的工作已失去了兴趣。
It seems [appears] that he is very tired. 他似乎很累了。
为避免重复，appear和seem后接的 that 从句有时可用so, not 代之：
“Is he reliable? ” “It seems [appears] so (not).”“他可靠吗?”“似乎是可靠的(不可靠)。”