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# 2.5: Colons

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The colon: well-loved but, oh, so misunderstood. The colon is not just used to introduce a list; it is far more flexible. The colon can be used after the first word of a sentence or just before the final word of a sentence. The colon can also be used to introduce a grammatically independent sentence. Thus, it is one of the most powerful punctuation marks.

The colon is like a sign on the highway, announcing that something important is coming. It acts as an arrow pointing forward, telling you to read on for important information. A common analogy used to explain the colon is that it acts like a flare in the road, signaling that something meaningful lies ahead.

Use the colon when you wish to provide pithy emphasis.

To address this problem, we must turn to one of the biologist’s most fundamental tools: the Petri dish.

Use the colon to introduce material that explains, amplifies, or summaries what has preceded it.

The Petri dish: one of the biologist’s most fundamental tools.

In low carbon steels, banding tends to affect two properties in particular: tensile ductility and yield strength.

The colon is also commonly used to present a list or series, which comes in handy when there is a lot of similar material to join:

A compost facility may not be located as follows: within 300 feet of an exceptional-value wetland; within 100 feet of a perennial stream; within 50 feet of a property line.

##### Practice

Is the colon used correctly in the following sentences?

1. Recently I had to convince my friend to save more of his pay check: he had spent most of his last one on art supplies.
2. He would buy, for example: art books, fancy pens, and different types of paper.
3. I told him that he shouldn’t buy art supplies in the following situations: (1) when he gets a random urge to buy more, (2) when he wants to get supplies he doesn’t need to complete a set, (3) when he gets supplies he won’t use “just in case” he ever needs them.
4. If he ever does need new supplies, he should: write down a list of things he needs, decide which things he can get at a lower price without affecting his art, and only buy a few things at a time.
5. I made sure that his spending limits were very exact: he couldn’t spend more than a third of his paycheck on art supplies.

[reveal-answer q=”201258″]Show Answer[/reveal-answer]
[hidden-answer a=”201258″]

1. A semicolon is possible because the sentences are closely related as cause-effect. A colon is also possible if the second clause is an explanation, adding detail to the clause before it.
2. Incorrect. A comma is the better choice for a short series or list. Normally, “for example” lists just a couple examples (a couple as an example of the larger list.)
• He would buy, for example, art books, fancy pens, and different types of paper.
3. Correct. A colon is used before a list. However, the initial word of the list item is lowercase if it is not a complete sentence.
4. Incorrect. No colon is used here because the part following the colon is neither an explanation nor a list; it is the completion of the central idea of the sentence. (No commas should be used either.)
• If he ever does need new supplies, he should write down a list of things he needs, decide which things he can get at a lower price without affecting his art, and only buy a few things at a time.
5. Correct. A colon is used before a second clause which explains or illustrates the first clause.

[/hidden-answer]

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