Is This a good way to start a sentence? It depends.
Chances are, you’ve begun many sentences with This. As long as it’s clear what This points back to, you’re in good shape. You’ll run into trouble, however, when This follows a sentence that contains several ideas, phrases, or clauses, because the reader may have trouble matching This up with one of those elements.
The two passages below both contain the following sentence: “This complicates our understanding of her religious views.” There’s nothing wrong with the sentence itself, and in the first example it works perfectly well, but in the second, it will leave the reader confused.
Emily Dickinson audaciously claimed that “[t]he Brain is just the weight of God—.” This complicates our understanding of her religious views.
Here, it is clearly Dickinson’s claim about the brain’s weight that complicates our understanding of her religious views. There is no need to puzzle this out by rereading the first sentence.
Emily Dickinson’s poem begins by declaring that “[t]he Brain—is wider than the Sky—” and concludes with the audacious claim that “[t]he Brain is just the weight of God—,” an ambiguous statement that seems to mean two things at once—that the brain is the exact weight of God and that it is merely the weight of God. This complicates our understanding of her religious views.
Here, we are left wondering, What is it that complicates our understanding of Dickinson’s religious views? The fact that she begins by comparing the brain with the sky and ends by comparing it with God? Her comparison of the brain with God? The ambiguity of this comparison? Or a larger idea conveyed by the sentence as a whole? It is impossible to be sure, even if we do go back and reread the first sentence.
There are many ways of revising the second sentence for clarity. Here are just two: (1) “This ambiguity complicates our understanding of her religious views”; and (2) “Dickinson’s claims about the brain complicate our understanding of her religious views.”
Rule of Thumb
If you think your reader may have to go back and reread an earlier passage to determine what This is, replace the pronoun with a more descriptive word or phrase. No sentence—whether it begins with This or not—should require readers to pick their way back over the prose that precedes it to grasp its meaning.
Dickinson, Emily. “The Brain—is wider than the Sky—.” Emily Dickinson’s Poems: As She Preserved Them, edited by Christanne Miller, Harvard UP, 2016, p. 273.