Understanding the difference between an independent clause and an introductory clause can help prevent punctuation errors and sentence fragments. The main difference is that the introductory clause will usually be preceded by an introductory word. Some examples of these words include before, after, though, during, when, and while. These words serve as a way of making a sentence richer in detail or adding time elements to a sentence.
Consider the following example of an introductory clause:
While Henry was doing the dishes, Janice was vacuuming the floor.
This sentence gives some details about time. We understand from it that Henry and Janice’s actions were being undertaken simultaneously.
You can also use an introductory clause to indicate contrasting ideas, as in this example:
While some experts believe that we can continue to use natural gas to solve our energy problems, others believe we cannot drill our way into a solution.
Here, the sentence presents two different viewpoints that more fully explain the material at hand.
The main mistake in distinguishing independent clauses from introductory clauses occurs when an independent clause is misdefined as something that can stand alone in a sentence. In both examples above, each introductory clause has a noun and a verb, which would make it seem like a complete sentence. It’s important to understand that the main difference between these clauses is that introductory or qualifying word that precedes the clause. You can use part of the introductory cause, “Henry was doing the dishes,” to make a complete sentence. Yet as soon as you add the “while,” to the beginning of either clause, it is not longer independent and will create a sentence fragment if you used alone.
An independent clause can be used entirely alone and depends on nothing else. “Janice was vacuuming the floor,” and “others believe we cannot drill our way into a solution,” can be lifted entirely and used as sentences. If these clauses began with before, while, when, after, though, or if, they would no longer make complete sentences.
One thing that you can do is to omit the introductory word. Our first example could become “Henry was doing the dishes and Janice was vacuuming the floor," which doesn’t change meaning dramatically. You can also separate these two independent clauses now that you’ve removed the introductory word and make them two sentences or two clauses separated by a semi-colon.
When you’re editing your work, look for those opening words that suggest dependence. You can omit them, but when you don’t, be sure a comma follows the introductory clause. Don’t forget to use an independent clause after the comma so that your sentence is complete.