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、後接不定式的問題
三者均可後接不定式，但 look 之後一般只限於 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、後接like的問題
look, seem 之後可接介詞 like，但 appear 之後一般不能：
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、用於進行時態的問題
appear 和seem不用於進行時態，但look有時可這樣用(儘管較少見)：
He looks [is looking] well. 他看上去氣色不錯。
但是不說He is seeming [appearing] well.
五、用於it開頭的句子
三者均可用於 it 開頭的句子，且三者之後均可接以 as if 或 as though 引導的從句，另外 appear 和 seem 之後還可接 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。
為避免重複，appear和seem後接的 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)。」