Marks are used intelligently only when each mark can give an intelligent answer to the reader who, meeting it on the printed page, challenges it with “What do you say to me?” This challenge may be made the supreme test of the value of any mark of punctuation.
The function of marks can best be shown by a study of their uses in illustrative examples:[2]
1. Respect the rights of children and their mothers will respect you.
No mark is required in this sentence to reveal its real meaning, for that is unmistakable; but almost any reader will momentarily mistake the meaning at the point where it seems to read as if written “the rights of children and of their mothers.” When the reader discovers that “the rights of their mothers” are not referred to, he is like a traveler who has taken the wrong road, and, discovering his mistake, must retrace his steps.
If a mistake has been made in reading this sentence, the reader must go back to the point where the mistake was made, and regroup the words. The process of regrouping the parts of a sentence is both distracting and tiresome when reading silently, and is very awkward when reading aloud.
The mistake is a mistake in grouping, that is in making one group of the words “children and their mothers” when these words are not so grouped by the meaning of the language.
We call “and” a conjunction, that is, a grouping word. It naturally groups together the two words between which it stands, especially if they make sense when so grouped. If these words are not to be thus grouped, the reader will be helped by having notice to this effect at the point where a wrong grouping may be made. We place a sign-board to guide a traveler; and one is equally useful to guide a reader. A mark of punctuation is the reader’s sign-board; and it is to be read for its directions.
As we cannot well discuss at this point in our study the proper mark to use in Sentence 1 we may select the comma, leaving the reason for the selection to be considered later. Thus the sentence written with a sign-board, is as follows:
1-1.[3] Respect the rights of children, and their mothers will respect you.
The answer to the challenge, “What do you mean?” put by the reader to the comma in this sentence, would be somewhat like this: “Reader, ‘and’ is not to be followed by a word with the same relation to ‘of’ that ‘children’ sustains to ‘of.’” In other words, “and” does not form the very simple group of words that it appears to form without the comma: it forms a new group.