The Period
In America, we call the tiny little punctuation mark that ends a sentence a period, but in other English-speaking countries they call it a 'full stop', which is probably a better description of the period's purpose. We don't need to spend much time discussing what a period does, since you already know: it lets the reader know a sentence is finished. Full stop.
The Colon
The colon, as you can see, is a little different. It looks like two periods stacked on top of each other. When an old Greek dude named Aristophanes of Byzantium invented this system of punctuation, there were originally three dots looking like this, each with a separate meaning.
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The high dot, periodos, indicated a complete thought - that is, the full stop - while two lower dots were called kolon and telia, and both indicated that only part of a complete thought was being expressed. Since English borrows its tricks from many languages - ancient Greek included - this vestige of punctuation remains. Only now, two dots means we're left with only part of a complete thought, while a single dot (the period) tells us the thought is ended.
The colon, therefore, is a way of letting the reader know there's more to come to further illustrate a thought after the main clause. This is usually in the form of a list, as follows. 'Dennis brought along several items with which to win the lady's heart: flowers, fresh fish, a record of death metal sea chanteys, and a tuba.' The sentence could end after 'heart,' but the colon adds the additional information of what kind of items Dennis brought.
Similarly, a colon can be used to introduce not just lists, but entire clauses that add important additional explanation. For instance, 'Today was turning out like one of his nightmares: everyone was frowning and no one was wearing any pants.' In this case, the colon introduces the information of what one of his nightmare was like.
Colons are also used to title or subtitle works, which is really just another way of adding additional information related to the focal point of the sentence. As in, The Zombie Who Wouldn't Eat Brains: A Children's Story. The first half of the sentence is the title, while the colon introduces additional information in the subtitle, which is that the book is a children's story.
The Semicolon
Author Kurt Vonnegut once wrote, 'do not use semicolons...all they do is show you've been to college.' He meant that as a chastisement to young fiction writers for being too pretentious and not plain-spoken enough in their writing, but since you're following this course, you're either in college or trying to get into college. So, you can do much worse than learn how the semicolon is used! And whether are not they're good for fiction, the semicolon can be very helpful in your formal writing.
So, the basics...a semicolon is used:
- To connect two independent clauses that are closely related to each other
- To connect transitional words and phrases within a sentence
- To keep items in a list that have internal punctuation separate
Connecting Two Independent Clauses
An independent clause is a clause with at least one subject and one verb that can stand on its own as a sentence. That means independent clauses can end with a period and still be grammatically correct. The independent clause can also be connected to dependent clauses or other independent clauses to form longer sentences. When connecting two independent clauses you can use a comma with a conjunction or a semicolon. When you choose to use them is a decision of style, so let's look at a few examples.
- 'Cecilia's favorite animal was the narwhal. She loved it mostly for its unicorn horn.'
- 'Cecilia's favorite animal was the narwhal, and she loved it mostly for its unicorn horn.'
- 'Cecilia's favorite animal was the narwhal; she loved it mostly for its unicorn horn.'
Each of these sentences is perfectly correct grammatically, but the way they appear on the page - more than the way they sound when I read them - makes a different impact on the reader. In the first example, there's a definitive break making the two ideas separate, even if they're thematically connected. In the second example, the conjunction actually makes the sentence feel a little stiffer, as if the writer is trying to jam the two ideas together. In the third, where the semicolon comes into play, it reads aloud basically the same as the first sentence but without the full stop of the period and subsequent capitalization of the word 'she.' So, the relationship between the two clauses is much chummier.