Subordination, the grouping of ideas into principal and subordinate clauses in a sentence, is much like the pictorial artist’s emphasis upon one element in his painting at the expense of all others; or like the photographer’s selective focus, by means of which he keeps a certain part of his picture in focus and deliberately allows all other elements to assume an out-of-focus fuzziness.
The use of subordinate clauses and of phrases is a writer’s way of telling his reader what thoughts are secondary to the important idea of his sentence. Here the dreary hours spent in clausal analysis of sentences should come to our help. Indeed, those hours of drill should have come to our help long ago; unfortunately, too few people understand that exercises in clausal analysis are not an end in themselves. Instead, separation of correctly subordinated sentences into their parts is only a preparation for building properly subordinated sentences for ourselves.
A sentence, as we learned long ago, is a complete thought expressed in words. It consists of only one thought; the thought may comprise several related ideas, so placed that their relationship is obvious.
Subordination is both a logical and a grammatical device by means of which a writer makes clear the relation among the ideas in a sentence.
For an example, start with an especially bad sentence, consisting of two ideas connected by and.
Jonson was an Elizabethan dramatist, and he wrote The Alchemist.
This sentence is loose, disjointed, and unarticulated, like a sprawling puppet whose strings have been dropped. Of the two ideas in the sentence, one must be more important to the writer’s purpose than the other. Is he writing of Jonson, the Elizabethan dramatist, or of Jonson, author of The Alchemist? Only the writer himself knows. He must tell the reader; he cannot expect the reader to make the distinction for him.
He could subordinate one of his ideas by writing,
Jonson, who was an Elizabethan dramatist, wrote The Alchemist;
Jonson, who wrote The Alchemist, was an Elizabethan dramatist.
His choice depends upon what he wants to say.
Either of these two forms is greatly preferable to the original. Reduction of one principal clause to a subordinate clause has shown the relation between the two ideas, one of greater, one of lesser, importance. The first step in subordination, then, is to express important ideas in principal clauses and subordinate ideas in subordinate clauses.
A careful writer will not be satisfied with what we have done with the bad sentence. He will probably want to use one of these variations:
Jonson, an Elizabethan dramatist, wrote The Alchemist,
Jonson, author of The Alchemist, was an Elizabethan dramatist.
Now further reduction of one of the ideas to a phrase has thrust it completely into the background as an unimportant, though relevant, idea.
This reduction of subordination ideas to expression in subordinate clauses or in phrases is founded on the important consideration that a writer must not expect his reader to sort out ideas; the writer must do the processing himself. He must assemble his ideas, sort them, and express them in such a manner that the reader will immediately see the relation among the ideas in the sentence.
Robinson, Berton. 1963. 12 Steps to Effective Writing. Chapter 3.