一、基本区别

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。

This seems to be a happy solution. 这似乎是一个理想的解决办法。

但是不说He looks to have traveled a lot.

三、后接like的问题

look, seem 之后可接介词 like，但 appear 之后一般不能：

He just looks like his brother. 他的模样就像他的哥哥。

He 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)。”