Sentence 7-2 suggests two uses of the comma to be found in the simplest sentences, one of which uses we almost take for granted, and the other is a mooted use. Why do we use the comma between nouns standing together? and why do we omit it before the first “and,” and use it before the next “and,” in the second group (the insane, feeble-minded, deaf and dumb, and blind)?
We answer that each use is based upon the fundamental principle of punctuation, the principle of disjunction, which distinguishes between the apparent and the real meaning of words or groups of words standing together.
It may be said, with apparent good reason, that no comma is absolutely necessary to separate the second and third nouns in such a group as “wheat, corn, and oats”; and it is quite common practice not to use a comma before the final “and” in such a group. While this practice may be correct, it is to be remembered that we are seeking helpful punctuation, not the absolutely necessary in each instance; and the most helpful punctuation is that which is most nearly uniform in its treatment of cases falling into well-defined classes.
As we are now considering what is technically called a series, it is well to consider the value of consistency in the punctuation of a series. A few examples will illustrate this point:
8. William Henry and James are at school.
The words in the above stand in the natural order and relations to express thought in almost the simplest form of language. “William” is a noun sustaining to “Henry” the adjective relation, just as it would do in the name William Smith, even though our grammars give it another relation. If we do not wish it to stand in this relation and to convey this meaning, we disconnect the two words by a comma:
8-1. William, Henry and James are at school.
This sentence names three boys; and its meaning is unmistakable at a glance.
We saw in Sentence 1 the tendency of the reader to combine in one group words connected by “and,” which is the natural manner of reading. Because of this fact, notice is to be given by punctuation when “and” does not connect the words between which it stands, unless notice is given in another way, as it often is. As Sentence 8-1 is written, “Henry and James” appears to constitute a group to be followed by other words in a series, just as is the case in the second group of No. 7-2. This tendency to wrong grouping will be seen in reading the following sentence:
8-2. Among the earliest colleges established in America were Yale, Trinity, William and Mary, and Harvard.