This is why. This is why you should beware of starting sentences with “this.” When you do this, your meaning will be somewhat vague. When you don’t do this, your meaning will be more clear.
“But wait,” the grammar cop objects, “this is only unclear because you started the entire post with an antecedent-less ‘this.'” My response: what’s unclear?
“This” requires an antecedent. “This” is a rearview mirror — it points to an object in its wake; an object to which it refers; an object which invests it with meaning, and without which it has none. So instead of depending on the rearview mirror, why not just reel the aforementioned object back into the car with you and let it ride shotgun in the sentence?
Then there are the instances where “this” is forward-pointing, like this: “This is my point: Using a backward-pointing ‘this’ at the beginning of your sentence often leaves the reader with at least a nip of ambiguity.” The forward-pointing “this” is much better because it anticipates soon-to-be-clarified future content instead of reflecting unclarified past content.
Of course, in the flow of reading, most of us won’t stop to think about what “this” means, and we’ll still get the general meaning. But we’ll still be drawing our own conclusions — i.e., making assumptions — about what “this” means. As a general rule, why not make this clear?
Do you do this often? If so, this will be the result: a level of antecedential ambiguity that will slow your reader mentally.
Here’s an example:
Yesterday the formerly esteemed Jim Tressel made national headlines when he resigned as head football coach at Ohio State University as a looming Sports Illustrated cover story threatens to blow the top off an alleged meth lab of NCAA violations brewing at Ohio State for the past decade. This reveals just one more scandalous piece of the increasingly ugly NCAA athletics puzzle.
What reveals just one more scandalous piece of the puzzle? Tressel’s resignation? Sports Illustrated‘s cover story? The alleged violation?
I wrote this (the sentence above), so I’m criticizing a mock illustration. But don’t you see this done often? No, not someone mocking their own straw man illustration — someone using “this” without a clear antecedent. See how ambiguous this can be?
So give this a shot: Try replacing “this” with the concept or action you’re really wanting to highlight, and see what it does.
What do I mean by “it”? Don’t get me started.