but 作“除……外”解时是一介词。它的语气没有 except 那么强，常用在下列一些词之后： all 以及由 every 和 any 起首的复合词； who, what, where 等疑问词； nobody, nothing 等否定词。现举几例如下：
(1)All but him were drowned.
(2)I will do anything but that.
(3)Who but a mad man would administer a deadly prison.
(4)It hurt nobody but himself.
(5)It's nothing but a joke.
except 是一简单介词，它的本义是“除去”或“不包括”，一般常用于表同类词语之间的关系，并常与all, every, nothing （或 nobody, none）, any 等不定代词连用，如：
(6)We all went except him. （him 与 we 同类）
(7)He works every day except Sunday. （Sunday 与 day 同类）
(8)We saw nothing except sea. （sea 与 thing 同类）
except 之后除可接名词和代词外，亦可接其他一些词语，如：
(9)I looked everywhere except there. （except 后接副词）
(10)I can take my holidays at any time except in August. （except 后面接一介词短语）
(11)I've done everything you wanted except make the beds. （except 后可接带 to 或不带 to 的不定式短语）
(12)He shared most of her ideas, except that his were more radical. （except 后接一从句。注意 except that 也常被看做一短语连词）
except for 是一短语介词，它由连词 except +介词 for 构成，其本义是“除去由于”，但通常皆译为“除去”，与 except 的意思似乎相同了，而这正是使中国学生感到困惑的主要原因。其实，在一般情况下，except for 的用法与 except 是很不相同的。首先 except for 一般不表同类词语之间的关系，而是表一整体中除外性的细节（即局部否定），如：
(13)The bus was empty except for one old lady. （bus 与 lady 不是同类词语， except for one old lady 表一除外性的细节）
再如：
(14)The wall was bare except for a picture of Chairman Mao.
但请注意 except for 有时意谓“除去为了”，如：
(15)He didn't give her money except for food. （except for food 在此意谓“除了买食物的钱之外”）
其次， except for 也常相当于 but for, 意谓“要不是（由于）”，如：
(16)Except for you I would be dead.
(17)She would have left her husband years ago except for the children.
再次，英美人往往将 except for 与 except 不加区别，混同使用（但except for 只可用在名（代）词之前，如例（16）、（17），而这也是使中国学生感到困惑的一个原因。但一般说来，except for 可置于句首，而 except 在习惯上不用于句首。但 “except 不可置于句首”的说法也不可绝对化。实际上，破例地将 except 置于句首的情况也是有的，如：
(18)Except a few mediocre pieces of fiction, his major literary works were rather successful.
最后，前已指出，except for与 except 的不同还在于 except 是一简单介词，而 except for 则是由“连词 except+介词”构成的短语介词之一。那么，自然也有由“连词 except +其他介词”构成的短语介词。现举几例如下：
(19)We went nowhere except to school.
(20)Except during one or two bouts of illness, such a thing never happened.
(21)Borer was forgotten, except by the few who had known him.
(22)Devon was both scholarly and very athletic, so the playing fields were vast and, except at such a time of year, constantly in use.
excepting 是由动词转化而来的分词介词（有些词典只将它看作分词），较为正式，有较强的动态意味，其含义是“把……除外”。在用法上，它与简单介词 except 之不同之处在于：
1. excepting 之后常只用名词或代词，并可置于句首，如：
(23)He answered all the questions excepting the last one.
(24)Excepting Sundays the stores are open daily.
2. excepting 常用在 not, without, always 等词之后，而except 则一般不能这样用，如：
(25)All men are fallible, not excepting the Pope.
(26)Those cars are reliable, always excepting the old red one.
except that 是一复合从属连词，似乎较为文气，如：
(27)She knew nothing except that he was there.
