Dangling Modifiers
Dangling modifiers: Your teachers in the past may have accused you of writing them from time-to-time; mine certainly have. A dangling modifier is just like a misplaced modifier except that the thing it's supposed to modify is missing! The modifier sits alone, modifying nothing, dangling its feet off the edge of a cliff.
Don't leave it hanging! Here's an example:
Dreaming of the future, the possibilities were limitless.
Well, that sounds really nice, but who's dreaming here? Someone? Everyone? We don't know, hence the modifier 'dangles.'
Sentences with dangling modifiers often start with a gerund verb (ING word), preposition or descriptive phrase. Even professional writers do it once in a while (though they certainly don't mean to).
Take this example from the New York Times Magazine:
If elected, Obama's main opposition will not come from Republicans.
If elected is the modifying phrase here, but again, it appears unclear what it's modifying. Is Obama's main opposition getting elected? Clearly, the writer meant Obama. Here's the simple fix:
If Obama is elected, his main opposition will not come from the Republicans.
In Real Life
In real life, not all examples of misplaced or dangling modifiers will be simple. Always ask yourself: Is the meaning of the sentence completely clear? This can be tricky because when people speak, they often make these kinds of modifier errors, and human brains are so good at picking up and understanding language that we can continue a conversation just as easily as if the error hadn't been made at all. Most of people's frustration with learning the nuts and bolts of composition and grammar comes from this process.
When you're talking face-to-face with someone, you're not only hearing the words that are coming out of their mouths, but you get additional information from their tone of voice, their facial expressions and their gestures. Plus, they exist in a certain context (your school, your home, the grocery store), and maybe you and the person even have a shared history that gives you even more possible information for understanding. All of this is going on in your background and helps lend to your understanding of sentences that might, otherwise, be confusing.
Take this sentence, which I'm sure you've heard before:
I just made it to class before the time-management presentation began.
This is a sentence with a misplaced modifier, but you know what it means, right? I'm telling you that I made it to the session right before it started, or before I had to do something important. But let's look at the simple modifier here -- that's just. Modifiers modify whatever they are directly next to, in this case made. But in this context, what does just made really mean? You're not physically constructing something. But the phrase is so common it may not feel wrong to you. Here's the correct version:
I made it to class just before the time management presentation began.
In the first version, while you may have a sense of what it means, this version has a much clearer meaning. How soon before the presentation began? Just before - which is much clearer than whatever just mademeans.