Consider this sentence: Like many people, I imagine, I worry about not having enough money for retirement. Why are the words I imagine set off with a pair of commas, and why are those two words placed where they are? Why not elsewhere in the sentence?
Commas cut, or better, they separate elements which would otherwise be read together, changing the meaning at least enough to slow readers down, if not confuse them outright. With the words I imagine bounded with commas, the sentence means I worry about not having enough money for retirement and I imagine many other people do too. Without the commas, however, the very same words mean something quite different: I worry about not having enough money for retirement like many people I imagine, which is to say that I am imagining many people, and like me, those people I’m imagining worry about not having enough money for retirement.
The commas, then, create what is called a parenthesis, an aside, or superfluous comment, which stands outside the logic and grammar of the sentence itself. We think of the word parenthesis (or the plural parentheses) first as the familiar punctuation mark, but the same term also refers to this way of stylizing a sentence. A parenthesis in this rhetorical sense brings a more natural, conversational tone to the statement, because our spontaneous exchanges rarely move in as straight a line as our written words must. But that pleasant, more natural tone will come at a steep price if we do not indicate with punctuation that the words we’re adding are merely a digression. In addition to commas, we can sometimes show such a digression with the punctuation marks we call parentheses, as in Like many people (I imagine), I worry about not having enough money for retirement, or sometimes even with a dash, though we can quickly see that here a dash would be over the top: Like many people—I imagine—I worry about not having enough money for retirement.
But where then to put this parenthetical aside? Our original version places it a few words into the sentence and right after the phrase it most directly modifies (many people). This positioning shows that the writer got going in a thought, then stepped outside that thought for a moment to say something about what he had just said, and then returned to the syntax to resume the real assertion he was making. That is what we do in conversation all the time, and so we can justifiably conclude that the writer’s relationship to the idea was, at least here, unalarmed and perhaps even resigned, because the sentence did not exhibit a strict compositional formality. Had, instead, those same two words been placed later in the sentence (Like many people I worry, I imagine), the writer would have been conceding reluctantly that he worries about not having enough money, not that he merely finds himself in the company of others with the same concern. Companionship is one thing, mental turmoil quite another.
All this is, moreover, a touchy topic, because our choice will depend on the mood we’re in—who we are—as we’re writing and revising the sentence, and committing to its assertion. Strange to say, but the words we choose and how we compose and punctuate them show our relationship to the ideas we’re communicating. Change the design and structure of a sentence and you change not only its meaning, but also its look and purport, in just the same way as the clothes we wear can signal much about who we mean to be. That close relationship between form and content is why the study of language has traditionally been regarded so important in education, because without some awareness of just what we’re implying with our words, we can confuse sometimes not only others, but worse, ourselves.