一、是把两个独立子句连接成一个句子。
二、是作为一个超级逗号。
三、独立子句是可以成为完整句子的一串单词。把两个完整的句子连接成一个长句时，可以在它们之间加一个分号。
Example:This could be a complete sentence;this could be another one.（例如：这边的可以是一个完整的句子；这边的可以是另一个。）
Example:Twelve workers started the project;only five remain.（例如：这个项目开始有12个工人，留在那里的只有5人。）
扩展资料：
次要用法
有几个比较少见的的情况也要求使用分号。
当在完整句的连接词语如“that is”、“for example”或“for instance”的前面列出3个或更多的条目时，你可以使用逗号或分号。下面的两个例句中的每一个，都是正确的。
Example:
Be sure to watch out for grammar errors,for instance,comma splices,run-on sentences,and dangling modifiers。
即使分句之间已经用了连词来连接，只要第一个子句里已经有了一个或多个逗号，也可以使用分号来连接两个中间已经加了连词的两个完整子句。 但它是可用可不用的，有时用了分号会使句子更容易理解。
Example:When I eat alone,I leave a mess;but that's not the worst of it.（例如：在我独自一人吃东西的时候，我会弄得一片狼藉，但这还不是最糟糕的事情。）
上面所提到的分号的次要使用方法是可用可不用的，所以你只要记得前面的使用分号的两种情况，你就决不会把分号放错了位置。
参考资料：百度百科-分号
本回答被网友采纳一般说来，分号的作用介于逗号和句号之间，即用分号隔开的两部分之间的关系，比用句号隔开的紧密，但不及用逗号分开的紧密。
1）用于并列句之间。
例句：
People make history; unusual people make history interesting.
Your car is new; mine is six years old.
2)分隔已有逗号的并列成分，以避免歧义。
例：
Follow this procedure：first，get your application forms; next, fill them out; last, pay the charge.
3)用于由for example, namely, in fact等引出的分句之前。
例：
Tom is well-liked; in fact, he is the most popular person in the class本回答被提问者采纳
分号有时又称为小句号。它表示一个停顿，其停顿时间在逗号与冒号的停顿时间之间。文章如采用许多分号，其风格则变得严肃、正式。为了正确使用分号，有必要先学会辨认主句。当两个主句没有任何连接词（and, but, or, nor, for）连接而出现在同一个句子里，这时最好采用分号使之分离。分号的主要作用很简单，它常用于分离没有连接词连接的句子。但最好不要在从句之间形成如此之强的停顿。如果你要连接从句，而又不愿意用连接词时，则采用分号。
The world is a comedy to those that think; a tragedy to those that feel.
You don't write because you want to say something; you write because you've got something to say.
In the past, boy babies were often dressed in blue; girls, in pink.
Can't you see it's no good to go on alone; we'll starve to death if we keep traveling this way much longer.
John F. Kennedy said at his inaugural speech, "Ask not what your country can do for you; ask what you can do for your country."
Our power to apprehend truth is limited; to seek it, limitless.
Science needs to be lived alongside religion, philosophy, history and esthetic experience; alone it can lead to great harm.
下列各词和短语如用于连接复合句时，常与分号连用：
then however thus furthermore
hence indeed consequently also
that is nevertheless anyhow in addition
in fact on the other hand likewise moreover
still meanwhile instead besides
otherwise in other words henceforth for example
therefore at the same time even now
例：
Being clever and cynical, he succeeded in becoming president of the company; meanwhile his wife left him.
The weather was cold for that time of the year; nevertheless, we set out to hike to the top of that mountain.
According to one national survey, high school boys expected a starting salary of $19,500 for their first full-time job; on the other hand, high school girls expected a starting salary of only $15,000.
thus,
however,
therefore一起使用(放在这些词语之前)。如
I
realize
I
need
exercise;
however,
I’ll
lie
down
first
to
think
about
it.
2.在句子中如果已经使用过逗点，为了避免歧义的产生，就用分号来分隔相似的内容。如
The
employees
were
Tom
Hanks,
the
manager;
Jim
White,
the
engineer;
and
Dr.
Jack
Lee.
需要注意的是：一个完整的句子以大写字母开始，以句点结束。写英文时用逗点代替句点、分号、冒号或破折号叫“逗号错”，这正是中国学生所要避免的。请比较下列例句：
误：It
was
raining
hard,
they
could
not
work
in
the
fields.
（注意：上面句子中划横线的部分是两个不同的主语，而且逗点前后的句子是完整的-----单独拿出来都能代表一个完整的意思。因此，用逗号违反了英文规定，即一个句子只能有一套主干。）
正：It
was
raining
hard;
they
could
not
work
in
the
fields.
It
was
raining
hard.
They
could
not
work
in
the
fields.