If the writer finds that he has written a series of sentences of the type described, he should recast enough of them to remove the monotony, replacing them by simple sentences, by sentences of two clauses joined by a semicolon, by periodic sentences of two clauses, by sentences, loose or periodic, of three clauses—whichever best represent the real relations of the thought.
[15.] Express co-ordinate ideas in similar form.
This principle, that of parallel construction, requires that expressions of similar content and function should be outwardly similar. The likeness of form enables the reader to recognize more readily the likeness of content and function. Familiar instances from the Bible are the Ten Commandments, the Beatitudes, and the petitions of the Lord's Prayer.
The unskillful writer often violates this principle, from a mistaken belief that he should constantly vary the form of his expressions. It is true that in repeating a statement in order to emphasize it he may have need to vary its form. For illustration, see the paragraph from Stevenson quoted under [Rule 9]. But apart from this, he should follow the principle of parallel construction.
| Formerly, science was taught by the textbook method, while now the laboratory method is employed. | Formerly, science was taught by the textbook method; now it is taught by the laboratory method. |
The left-hand version gives the impression that the writer is undecided or timid; he seems unable or afraid to choose one form of expression and hold to it. The right-hand version shows that the writer has at least made his choice and abided by it.
By this principle, an article or a preposition applying to all the members of a series must either be used only before the first term or else be repeated before each term.
| The French, the Italians, Spanish, and Portuguese | The French, the Italians, the Spanish, and the Portuguese |
| In spring, summer, or in winter | In spring, summer, or winter (In spring, in summer, or in winter) |
Correlative expressions (both, and; not, but; not only, but also; either, or; first, second, third; and the like) should be followed by the same grammatical construction, that is, virtually, by the same part of speech. (Such combinations as “both Henry and I,” “not silk, but a cheap substitute,” are obviously within the rule.) Many violations of this rule (as the first three below) arise from faulty arrangement; others (as the last) from the use of unlike constructions.