Summary
Dashes, colons, and semicolons connect two independent clauses that are related in thought.
What can they do for my writing?
Essentially, semicolons, colons, and dashes offer you different ways to join your ideas together, and you can use them to adjust how you want your sentences to sound. A comma between two independent clauses creates a run-on sentence that doesn't give enough definition between your ideas, while a period between them sometimes distances them too much. Connecting your clauses with a semi-colon might provide a pause that is just right, while a dash could make that pause more dramatic by highlighting the following clause, or a colon could signal that the second clause expands on the first. But remember that when deciding whether to use a period or a semi-colon, a colon or a dash, it is more a stylistic/rhetorical choice than a choice of right or wrong.
How do I use them properly?
1. Dashes
Quick Use: Use a dash to connect independent clauses or to interrupt a main clause in a way that creates dramatic effect.
Dashes function in two ways: to signal interruptions in a sentence (basically like parentheses), and to connect independent clauses. But if the first function can be substituted with parentheses and the second with a semi-colon or conjunction, then why use dashes instead? The effect of dashes is that they highlight the clause that they are inserting, thus bringing attention to it.
There's always a second chance – even for someone like you – so don't think your career is at an end.
I know you are still there – somewhere in the sky.
2. Colons
Quick Use: Introduce a list or quotation, or connect two clauses in which the clause after the colon details or expands on the first.
You might be most familiar with colons being used to introduce a list of items or a quotation.
These are my favourite childhood memories: walking with my grandfather, picking apples in the fall, and opening gifts on a cold, Christmas morning.
In expressing the weakness of divine right, Richard II connects wall imagery to the image of a crown:
'...for within the hollow crown
That rounds the mortal temples of a king
Keeps Death at his court, and there the antic sits'
(III.ii.160-2)
Just one rule to remember here: when listing things do not put the colon after an incomplete sentence unless the end of the sentence signals that a list is coming.
Here's what I want: chicken, oregano, and lemons.
(Complete sentence, followed by a list)
OR
I want the following: chicken, oregano, and lemons.
(Incomplete sentence with signalling word)
NOT
The things I want are: chicken, oregano, and lemons.
(Incomplete sentence with no signalling word)
Another way that colons are used is to connect two clauses, but only when the following clause gives an example or expands on the previous one. In these circumstances, a colon serves as a substitute for a word like 'namely' or 'that is'.
There was a book I especially loved from that class: the Pillowbook of Sei Shonagon.
She finally did what she never thought of doing her entire life: pursuing a degree in photography.
3. Semicolons
Quick use: Join independent clauses together in a way that emphasizes their connection.
The easiest way to think of a semicolon's use is to think of it like variations on a period. However, whereas periods separate two ideas, a semicolon bring them together. In this way, you can emphasize that two ideas are related to one another in an important way, rather than having them exist as two independent thoughts. Just remember: if you can't use a period, you can't use a semicolon.
There was no one left; the kitchen counters and the dining chairs were empty, and only the faint memory of laughter remained.
There isn't a right or wrong when it comes to choosing between a semicolon and a period; the choice is a stylistic one.
The semicolons in the examples above join two complete sentences to stress how they are connected. See what happens when either a period or a comma is substituted:
There was no one left, the kitchen counters and the dining chairs were empty, and only the faint memory of laughter remained.
There was no one left. The kitchen counters, the dining chairs were empty, and only the faint memory of laughter remained.
In the first sentence, the choice comma has created a comma-splice, which is a grammatical error. The second is grammatically correct, but intentionally puts a silence before the following thought to give a different kind of emphasis to the thought expressed.
While semicolons, colons, or dashes can connect two independent clauses by itself, you can also throw in a conjunction to make the relationship between the two independent clauses clearer.
A sadness hangs in the plants that are dying for the winter; but take heart, young one, for they will bud anew in the spring.
In this case, the conjunction 'but' makes it clear that the relationship between these two clauses is one of contrast. You could use a comma instead of a semi-colon with the conjunction to make a grammatically correct sentence. Rhetorically, however, the semicolon puts in a little more delay that works well in the context of the sentence. The sentence above would probably be more effective if read slowly and carefully; the semicolon slows it down more than a comma would.
