In my days as an instructor of basic English composition, I was often amazed at where students put commas. A comma might appear in the middle of a prepositional phrase or an infinitive. It could precede or follow a question mark or an exclamation point. At times, it seemed that students, while writing a composition, thought to themselves, “Gosh, this sentence I’m writing is getting pretty long, so I better put in a comma somewhere.”

So, when should a comma be used? Although the rules of grammar provide most of the answer to that question, the writer’s intent can also be a factor. That is the case with restrictive and nonrestrictive clauses. Consider the following sentence:

The honor roll students, who are visiting the college campus, should report to the principal’s office.

Are commas being used correctly here? It depends on what the sentence writer intends. If the clause set off in commas refers to all the honor roll students, then the commas are needed. “Who are visiting the college campus” is some extra information the sentence writer wishes to add about the whole group of honor roll students. But suppose some honor roll students are staying in class and not visiting the college campus. In that case commas should not be used.

The honor roll students who are visiting the college campus should report to the principal’s office.

Here, the clause “who are visiting the college campus” is restrictive. The sentence writer is saying, in effect, there are a number of honor roll students, but only those who are visiting the college campus should report to the principal’s office. The honor roll students who aren’t visiting the college campus can stay in class. To put it another way, the clause restricts the range of honor roll students to those who are going to the college campus.

Now let’s create a more-provocative sentence: 

The boxing team members, who are pretty stupid, are not likely to graduate.

That sentence could get you into trouble with some tough guys, because with the commas setting off the clause “who are pretty stupid,” you are referring to all members of the boxing team — no exceptions.  Uh oh! Better get rid of those commas or be prepared to get into the ring.

The boxing team members who are pretty stupid are not likely to graduate. 

That might keep you out of harm’s way because now the clause is restrictive. Only some members of the boxing team — those who are stupid — are not likely to graduate. There are also smart members of the boxing team, and they are all but guaranteed a diploma. 

There are other ways commas can change the meaning of sentences, and future posts will explore those ways in more detail. I’m sure my blog readers, who are intelligent people, will learn much from these posts.