There are rules in English, and there are rules that are not quite what they seem. Today we look at one of them.

Last week during Dan Rodricks’ Midday program for National Grammar Day, Margaret Benner, director of the writing support program at the English department at Towson University, objected to what she identified as an error in the first set of sample questions.

These are the sentences:

a. We should be careful in our writing, since people judge us on our grammar.

b. We should be careful in our writing, because people judge us on our grammar.

The point of the question was to get at an artificial distinction that some people make between since and because, saying that since is only permissible in temporal statements, not causal ones. Ms. Benner raised a separate point, insisting that a dependent clause that follows a main clause, as in the sentences above, must not be set off by a comma. That is an error, a violation of a rule, she said.

She commented further on this blog:

I sent an email to the WYPR broadcast yesterday about the errant comma used in the first sentence given in the grammar quiz. You answered that the comma was allowed: Some commas, you said, come under the heading of "rules" while others are "discretionary." It's true -- I'm an English teacher and probably too tied into my rule-ish-ness, but do you know how many students have argued over their right to place a comma wherever they want because "there's a pause there"? In other words, it's "discretionary." I don't want to belabor the point, but putting a comma in that first sentence in the quiz wasn't correct. It also wasn't discretionary -- or helpful to the meaning of the sentence. A discretionary comma might be used in a sentence such as the following: "Underneath, the papers were scorched." I'm not arguing against discretionary commas; I am only arguing for the valid boundaries of discretion.

I don’t want to belabor the point, either, and I certainly don’t want to accuse Ms. Benner of any kind of rule-bound rigidity. But I think that her point is about a convention, rather than a rule. Consider the advice from The Chicago Manual of Style:

Comma following a main clause. A dependent clause that follows a main clause should not be preceded by a comma if it is restrictive, that is, essential to the meaning of the main clause. If it is merely supplementary or parenthetical, it should be preceded by a comma. (Note that the distinction is occasionally tenuous; if in doubt, use a comma to indicate a pause.)

An example given: “He didn’t run, because he was afraid to move.”

When Chicago suggests that the writer can and should, in close cases, insert a comma “to indicate a pause,” the manual is endorsing the writer’s discretion. It seems to me to be more productive to consider this a convention or a guideline than a rule.

In the 18th century it was conventional to put a comma between the subject and predicate; in our time it is conventional not to do so. You can call this a rule, but it’s not quite like the rule that an appositive is set off by commas.

I think that the teaching of grammar and usage has not been well served by the multiplication of rules, some of which are actually rules, some of which are conventions, some of which are guidelines, and some of which are plainly wrong. Treating everything as a yes-or-no, right-or-wrong rule can make writing look like a mere application of a rulebook and deprive students of the flexibility of the language and the opportunity to develop taste and judgment.

A writer in English enjoys a considerable degree of discretion, particularly in the use of commas to indicate the rhythms of spoken language. If some students go overboard with this, it is a problem of stylistics, not grammar. If I choose to insert a comma in those two sample sentences to make sure that the person putting the question on the air pauses to emphasize that that is where the choice lies, I do not think that I am exceeding my authority.