No sooner do we recognize that a well-written sentence is clear and exact than we come upon good writers not saying everything they mean. Look closely at a perfectly fine sentence like she thinks the package will be delivered today, and you can see that something grammatical is not quite right: what does it mean to think the package? Not much, says the schoolmarm or martinet missing, as they often do, the forest for the trees. We know in our bones that she thinks the package means she thinks that the package, and we don’t stumble over a sentence when a word that is otherwise technically necessary has been omitted. But why is it all right to leave a word out if our goal is to be clear and exact?
The short answer is that the science of grammar makes no claim for flawless precision. Arising from our perception of things and events in the world, where change or movement is the only thing constant, language must rely on more than a mechanical application of unassailable grammatical rules. Grammar works in concert with reason and rhetoric, and the three together fashion sentences that carry both objective meaning and lived experience. And we don’t live, or shouldn’t live, in a mysterious world like inerrant robots.
So when we write she thinks the package will be delivered today, we have omitted the subordinating conjunction that in order to mimic our conversational voice and produce a more natural style. Subordinate conjunctions begin clauses which can then function as a part of speech. If we restore the conjunction that in our sentence (she thinks that the package will be delivered today), we can see that the conjunction marks the beginning of the clause which, in its entirety, is the direct object of the transitive verb thinks. This omission of a word that is otherwise grammatically or logically necessary is called ellipsis, and it is a very common feature of English. The term comes from a Greek verb meaning to fall short (an oval, or ellipse, is thought to fall short of a perfect circle), and it is one of a number of related rhetorical figures (syllepsis and zeugma are two others) that help us stylize our sentences to certain effects.
In speaking with others, we do not state every last word we mean. We rely on the attentive and largely sympathetic awareness of those involved to fill in, from the richness of our common human experience, what can reasonably be assumed in omission. We point to ideas without detailing each in full; we linguistically wink at one another, knowing that they will see the meaning and supply what is needed. Elliptical statements depend on a certain degree of sophistication, a shared knowingness that comes from our experience together in the world. It creates, ironically, a forcefulness by not saying every last thing, by pulling in the reader or listener to restore what is meant. Not to permit ellipsis is to capitulate to the hypercritical.
The trick, of course, is to know when something can be omitted and when it can’t. The legal language of courts and contracts sounds tedious because that is not the time to ask the reader to supply what has obviously been omitted: what is missing for the buyer might be very different from what is missing for the seller. But when circumstances are not so consequential and there is a need to accelerate a sentence through a well-know terrain of ideas, then the rhetorical device of ellipsis can have a very useful and sophisticated effect. Learning how and when to use it can be as frustrating as the answer an accomplished cook gives to just how much salt he put in that delicious soup, but in writing there is only one good answer: read and read and read.