used for saying that what happens next is disappointing or unpleasant。只不過卻 (表達出失望並且否定前句)
I tore open the box, only to discover that some of the parts were missing.
used to give a reason why something is not possible or true。要不是/但是 （否定前句，然而相較於 only to，不一定是失望，有時也用於慶幸）
要不是: They would all have died except for [=but for] her and her quick thinking. (否定前句，指出「事實上」他們沒死，既然和事實相反，那就要用 would have 假設語氣)
但是: I want to go, except that I’m tired. (否定前句，指出他沒辦法去）
We would like go, except (that) it’s too far. (否定前句，指出我們沒辦法去）
only that = except that
只不過: He is correct, only that some details are omitted.
只可惜: This suit fits me well, except that the trousers are too long.
used to introduce a statement that indicates the only person or thing that is not included in or referred to by a previous statement。這是 except 的正常用法，可以和 but 互換，作為連接詞，前面加什麼後面就加什麼。此外，他還能加個介詞來用。
He does nothing except [=but] complain. (動詞 except 動詞）
She didn’t leave the house all weekend, except to go to church.
Employees were not allowed to leave except in an emergency. [=unless there was an emergency]
Take no orders except from me. [=take orders only from me]
Everyone was invited except for [=but] me.
used to introduce a statement that adds something to a previous statement and usually contrasts with it in some way。然而（連接詞，不一定好或壞的對比用法）
She played well, yet she didn’t qualify for the finals. （轉壞）
He’s overweight and bald, (and) yet somehow, he’s attractive. （轉好，有時會加上 and 來中斷語氣）