A Dash of Style by Noah Lukeman

depend on each other? Does one build and the other reveal, or conclude? If not, remove the colon, or reconstruct the sentences so that each portion inherently feeds off the other.
    THE DASH is built to interrupt. It can strike with no warning, cut you off, stop conversations in its tracks, and redirect content any way it pleases. It is perhaps the most aggressive of all punctuation marks, and will grab the spotlight whether you like it or not. In fact, the word "dash" aptly derives from "to dash," or to shatter or strike violently.
    When discussing the dash, most grammarians find it significant only inasmuch as it should not be confused with a hyphen; often it is relegated to a sign of carelessness. What a shame. The dash is a beautiful, striking mark of punctuation, which can enhance creativity, and which is crucial for capturing certain forms of dialogue. The dash can, of course, indicate haste and sloppiness (as
    we'll see below), but it must first be taken seriously before it can be dismissed.
    Parentheses, on the other hand, respectfully interrupt you, so that you needn't cease speaking or change your train of thought. Their interruption is more of an enhancement, like a trusted advisor whispering in your ear. Like the dash, parentheses are often dismissed as a mere technical appliance. As with the dash, this is not where the discussion ends. Misused, of course, parentheses can be a terrible blight on a work, one that can make it nearly unreadable. But in the right hands, they can be a great creative tool, adding a layer of complexity to your text without interrupting its rhythm, one that could not exist any other way.
    No creative writer is complete without knowing how to call upon and master these two marks.
    HOW TO USE THEM
    To truly grasp how to use dashes and parentheses, we must examine them together, comparing and contrasting their similarities and subtle differences. They are both interrupters; they both propel their subjects into the spotlight; are both used to digress, elucidate, or explain; and they perform a nearly identical function when the dash is used in pairs. To consider these marks separately (as many punctuation books do) is a mistake. Not only do they perform overlapping functions, but we learn more about each by holding them side by side.
    • Dashes and parentheses are commonly used to indicate an aside or digression. Sometimes asides need to be interjected midsentence, whether to clarify or enhance. These asides could be removed and transformed into sentences of their own, but then you wouldn't achieve the same effect. Sometimes one needs to digress in the midst of a thought, in order to make the thought fuller or more complex. Such an aside takes a simple, straightforward thought and gives it a new dimension. Consider:
    Buffaloes roamed freely in the Midwest in the 1800s.
    This is a simple sentence. Using dashes or parentheses, though, we can enhance it, without requiring a new sentence. Consider:
    Buffaloes roamed freely in the Midwest (some say in the Southwest, too) in the 1800s.
    Buffaloes roamed freely in the Midwest in the 1800s—some say in the Southwest, too.
    The asides add something; at the same time, while they pull us in another direction, they are also close enough to the main thought that they wouldn't work as sentences on their own. They are really sentence fragments, half ideas, looking for a place to land and needing the assistance of a dash or parentheses to give them a home.
    In the above examples the parentheses and the dash, while serving the same purpose, went about it a different way. The parentheses allowed the aside to come in the middle of the sentence, while the dash demanded it be relegated to the end. This is implicit with the use of the solo dash, as it forces a clause to a sentence's end. Consequently, its effect is not exactly the same, since the aside following the dash feels more like an afterthought, and also prevents the sentence from carrying on. More