1. 從意思上看：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 的不確定性更大壹些。seem 側重指根據某種跡象作出的推斷，也不壹定是事實。
2. 從用法上看：
(1) 三者均可後接不定式，但 look 之後壹般只限於 to be (且較少見)。
如：
正：He seems [appears，looks] to be tired. 他好像很累了。
正：He seems [appears] to have travelled a lot. 他似乎去過不少地方。
誤：He looks to have travelled a lot.
(2) look, seem 之後可接介詞 like，但 appear 之後壹般不能。
如：
He looks [seems] like a fool. 他看起來像個大傻瓜。
(3) appear 和 seem 不用於進行時態，但 look 有時可這樣用。
如：
正：He looks [is looking] well. 他看上去氣色不錯。
誤：He is seeming [appearing] well.
(4) 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。
如：
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。
註：後接 that 從句時，有時可用 so，not 代之。如：
A：Are they reliable? 他們可靠嗎?
B：It seems [appears] so (not). 似乎是可靠的(不可靠)。
另外，比較以下同義句型：
It seems [appears] that he is ill.＝He seems [appears] to be ill. 他似乎病了。