Chapter Three: Rule Fifteen

III. ELEMENTARY PRINCIPLES OF COMPOSITION

Rule 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 10. 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. Many violations of this rule can be corrected by rearranging the sentence.

It was both a long ceremony and very tedious.
- The ceremony was both long and tedious.
A time not for words, but action
- A time not for words, but for action
Either you must grant his request or incur his ill will.
- You must either grant his request or incur his ill will.
My objections are, first, the injustice of the measure; second, that it is unconstitutional.
- My objections are, first, that the measure is unjust; second, that it is unconstitutional.

See also the third example under Rule 12 and the last under Rule 13.

It may be asked, what if a writer needs to express a very large number of similar ideas, say twenty? Must he write twenty consecutive sentences of the same pattern? On closer examination he will probably find that the difficulty is imaginary, that his twenty ideas can be classified in groups, and that he need apply the principle only within each group. Otherwise he had best avoid the difficulty by putting his statements in the form of a table.

Next: Chapter Three: Rule Sixteen