Sentence 1-1 is a good illustration of Diagram 2; and yet the apparent relation between “children” and their “mothers” might so strongly impress itself upon the mind of an inexperienced reader, especially if reading the sentence at sight and aloud, that the comma would not prevent a momentary wrong combination of these words. A semicolon before the conjunction would prevent the liability to such error, and probably do so even with the most inexperienced reader. Thus we have a choice between the comma and the semicolon in Sentence 1; and this choice rests upon the degree of liability to error, which cannot be the same with different classes of readers. Liability to error in grouping is increased by a closeness of apparent relations that are wrong relations, and also by a reader’s lack of expertness in grouping language at sight. In view of these facts, we think the use of a semicolon in Sentence 1 better punctuation than the use of a comma; but the use of the semicolon in this particular sentence should not be made to justify a rule requiring a semicolon between every two clauses connected by a conjunction, or between two clauses so connected, one of which contains one or more commas.
Our next sentence is taken from an essay, in a high-class magazine, by the professor of English in a leading eastern university; and this essay has for its title “Writing English”:
58. The boy must be able to say what he knows, or write what he knows, or he does not know it.
As written and punctuated, this sentence contains three apparently coördinate groups of words, the groups being connected by “or,” and the grouping indicated by commas. It is, however, composed of only two main groups, the first of the two groups being regrouped into other groups. Such grouping should always be shown by the punctuation; for, when it is not so shown, the sentence cannot be read without some distractive effect upon the reader and, if read aloud, also upon the hearer.
The failure of this sentence to read smoothly, or without distractive effect, arises from the usual cause: the form of the language leads the reader to look forward to a mode of development of the sentence which does not follow,—that is, the apparent mode of development, as exhibited in the grouping, is not the real mode of development. As each of the second and third groups is introduced by “or” and preceded by a comma, the reader is led to look for the same relation between the second and third groups that exists between the first and second. He is thus led to expect a group in a series, which does not follow.
The distractive effect of the sentence can be removed in some degree by writing it in the following form, the added “to” giving the second group a form similar to that of the first:
58-1. The boy must be able to say or to write what he knows, or he does not know it.
In this condensed form the sentence lacks, at the point of condensation, the emphasis of the original; and therefore the sentence is not so effective in its statement of a truth. If, then, the original form is preferred, its distractive effect can be removed by the use of punctuation that properly groups its parts:
58-2. The boy must be able to say what he knows, or write what he knows; or he does not know it.