冒号 Colon

Colons can be confusing, that's true, but their function is actually quite straightforward: they introduce related information. Let's take a look at these 5 rules of colon usage.

1. Use a colon to introduce an item, list or explanation, if the list comes after a complete sentence or independent clause. For example:

• There are three things every dog needs: food, water, and healthcare.
• This year I want to visit four amazing cities: Paris, London, New York, and Barcelona.
• Here's a temporary solution to dripping faucet: tie a string to it, and let the drops silde down the string to the sink.

2. Colons Separating Independent Clauses

A colon can be used to separate two independent clauses when
a) the second clause is directly related to the first clause (not just vaguely related) and
b) when the emphasis is on the second clause.

• A dolphin is not fish: it is a warm-blooded mammal.
• The research is conclusive: climate change is a reality.

这一点在SAT中比较有难，前后两句话必须要有很紧密的关系，并且重点在第二句话才可以用。
同等情况下，如果有分号或者句号，先不考虑用分号。

3. Use a colon to introduce a bulleted or numbered list. For example:

Today's a busy day, for we have five tasks at hand:

1. Writing Project
2. Listening Drill
3. Speaking Practice
4. Reading Note
5. Musical Composition

Note: capitalization and ending punctuation are optional for single words or short phrases in bullet points or numbered lists.

4. Use a colon to introduce extended quotations.

Use colons to introduce a quotation when it is not integrated into the syntax of your sentence or otherwise requires a formal introduction:

Nabokov opens his autobiography with a statement on mortality: “The cradle rocks above an abyss, and common sense tells us that our existence is but a brief crack of light between two eternities of darkness.”

But use a comma after a verb of saying (e.g., says, exclaims, notes, writes):

As Nabokov writes, “The cradle rocks above an abyss, and common sense tells us that our existence is but a brief crack of light between two eternities of darkness.”

No punctuation is needed when the quotation is integrated into the syntax of your prose:
Nabokov writes that life is “a brief crack of light between two eternities of darkness.”

5. Use a colon following a greeting (also known as a salutation) in a formal or business letter.

It does not matter if you are using the person's first name, both first and last name, or their title, you should always use a colon if the letter is formal. If the letter is personal, then either a colon or comma is appropriate.

• To Whom It May Concern:
• Dear Mr. Wilson:

考试陷阱：多余的冒号

误：Her two goals were: to lose weight and give back energy.
正：Her two goals were to lose weight and give back energy.
解析：冒号前句子不完整。

误：Its offerings include: IT Services, Engineering Services, Consulting Services, BPO Services, and Products and Platforms.
正：Its offerings include IT Services, Engineering Services, Consulting Services, BPO Services, and Products and Platforms.
解析：冒号前句子不完整。

冒号前需要一个独立句。一个句子如果结构不完整或意思不完整，那它的后面就不应该使用冒号。

练练手

更详尽的冒号用法