When we have trouble writing the sentence we want, or understanding a sentence someone else has written, the difficulty may lie all the way deep down into the system of language, where subjects and predicates connect with things and thoughts. A basic question we should always be prepared to pose, whether as a critical writer or reader, is What is this sentence about? That, however, can be deceptively simple to ask of a complex sentence when we’re not clear about some basics of grammar and logic.
There are three (some say four) types of sentences in English, and a sentence type is determined by the combination and character of its clauses, whether independent or subordinate. A simple sentence is composed of one and only one independent clause, a compound sentence of two or more independent clauses, and a complex sentence of at least one independent and at least one subordinate clause. (Those grammars which count a fourth type of sentence, called a compound-complex, are creating a separate category for what is really just an elaborated complex sentence. Three kinds should suffice for all practical purposes.)
A complex sentence, therefore, has at least two clauses of differing character, and that is what makes the question of what a particular complex sentence is about sometimes difficult to answer. Every clause, by definition, posits a subject, to which it joins a predicate (hence we speak of an assertion, whose original Latin verb means to join); so if a complex sentence has multiple subjects because it has multiple predicates, how are we to decide which subject and predicate will answer this important critical question?
Take, for example, this complex sentence of three clauses: Since my flight was delayed, I decided to revise my speech, which I would deliver later in the day. We might commonly answer that this sentence is about my flight, because that is the first subject we come to; or we might say a my speech, because that is the next noun and idea to jump out at us; or we might even say, though probably less likely, the day, again because that is a noun which draws a quick image for our mental vision to fasten on. Reading critically, however, means reading the constructive architecture of a sentence, which will avoid an impressionistic reaction to whatever word happens to attract our attention.
We must conclude, then, that this sentence is about my deciding something, because the subject I and the verb decided make up the independent clause of the statement. An independent clause represents the center of a sentence galaxy, around which orbit other subordinate clauses if the sentence is complex. Orbiting clauses, like the spokes attached to the hub of a wheel, are connected and arrayed in a logical formation in relation to the central assertion of the independent clause. This is important because we have a choice to make in composing a complex sentence: which assertion do we wish to assign as the controlling thought—the illuminating light—around which other thoughts take their logically supporting position?
In the example as we have it, the writer arranged the three clauses in such an order as to give first the primary reason for the central idea, then to state that central idea, and then to conclude with an additional, proximate reason. But the sentence could have been composed differently by changing the character of the clauses: My flight was delayed, and so I decided to revise my speech, which I would deliver later in the day. Under this revision, the original clause of reason has been converted into an independent clause, and the original central assertion has been shifted to a result clause, still an independent clause, but one now needing another independent clause logically to precede it. In the original version, the genesis of the sentence rose with the light of deciding something; in this revision, what first dawned on the writer was a flight delayed, which then illuminated the subsequent ideas.
And still other arrangements are possible: I would deliver my speech later in the day, and so since my flight was delayed, I decided to revise it (where the idea of delivering a speech is central). Or this: My flight being delayed, I decided to revise my speech, which I would deliver later in the day (where the idea of deciding something remains the controlling idea, but is introduced broadly with a nominative absolute phrase). Or this: I decided, since my flight was delayed, to revise my speech, which I would deliver later in the day (where the independent idea of deciding is interrupted by the reason for it). Each of these revisions changes the mass and balance of the thoughts which together light up one particular galaxy of discourse.
All this then points to the consequential observation that every sentence we write or read, especially every complex sentence, is the visible representation of value: the writer has chosen to place what is seen to be of central importance in an independent clause, and what is related and connected in some logical way to that idea in the subordinate clauses. With this knowledge of sentence structure, we can assure ourselves in revision that the relative value of one thought to another in a sentence is as we wish it, given our audience and purpose. Only in a simple sentence, where there is only one clause, do we avoid this question of relative, or gravitational, value, but even there the addition of phrases will pose a similar question. Our sentences communicate a galaxy of ideas, and every galaxy is a system, or organized structure, gravitationally bound together.
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