一、基本區別

look 指視覺印象，appear 指外表給人的印象，這兩者可能是真象也可能是假象，appear的不確定性更大一些，seem 側重指根據某種跡象作出的推斷，也不一定是事實。

二、后接不定式的問題

三者均可后接不定式，但 look 之后一般只限于 to be(且較少見)：

He seems [appears, looks] to be very tired. 他好像很累了。

He seems [appears] to have traveled a lot. 他似乎去過不少地方。

This seems to be a happy solution. 這似乎是一個理想的解決辦法。

但是不說He looks to have traveled a lot.

三、后接like的問題

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

He just looks like his brother. 他的模樣就像他的哥哥。

He seems like a fool. 他看起來像個傻瓜。

四、用于進行時態的問題

appear 和seem不用于進行時態，但look有時可這樣用(盡管較少見)：

He looks [is looking] well. 他看上去氣色不錯。

但是不說He is seeming [appearing] well.

五、用于it開頭的句子

三者均可用于 it 開頭的句子，且三者之后均可接以 as if 或 as though 引導的從句，另外 appear 和 seem 之后還可接 that 引導的從句：

It looks [seems, appears] as if he has lost interest in his job. 看來他對自己的工作已失去了興趣。

It seems [appears] that he is very tired. 他似乎很累了。

為避免重復，appear和seem后接的 that 從句有時可用so, not 代之：

"Is he reliable? " "It seems [appears] so (not)." “他可靠嗎?”“似乎是可靠的(不可靠)。”