Let’s jump into the deep end of the pool and see if we can keep our heads above water while we sort out a sentence that illustrates a common grammatical arrangement in English. One confounding characteristic of the language is that it often does not feel the need to say explicitly everything it means. That can leave us as readers or listeners with what appears to be a wave of onrushing words when we try to understand how a sentence is put together—something we ultimately want to be able to do in order to see the implications hidden in what we’re hearing or reading. Understanding the logical connection of ideas in language, though, takes a little practice.
The omission of words that are otherwise logically and grammatically essential is called ellipsis, and sentences that omit words in this way are called elliptical statements. If you are describing to me someone you met recently, I might by some coincidence suddenly say to you, I think I know the person you’re talking about. My reply would be a straightforward, casual comment, easily understood by any speaker of English, but not so easily understood grammatically. A first look at the sentence finds no fewer than three verbs: think, know, and are in the contraction you’re, and if we forget that every verb makes up a clause, we’re going to start sinking fast in our analysis. We’re saved by remembering that we’re not really examining a sentence; we’re trying to understand the composition of the clauses that comprise a sentence. With that realization we can divide or sectionalize a statement into more manageable divisions and proceed in a more orderly way.
The first clause we have is I think, and after identifying a clause, we should next ask what kind of verb the clause has, transitive, intransitive, or copula. We usually think something, and so we are safe to assume here that the verb think is transitive, which means it must govern a direct object, that element that will answer the question what? posed to the verb: what do you think? The answer to that question is the remainder of the sentence (I know the person you’re talking about), but that section, a clause in its own right, is not explicitly connected to the transitive verb for which it is an object. The connector we should be hearing or seeing is the subordinating conjunction that, but to say I think that I know the person you are talking about can sometimes be unnecessarily fulsome, and so by ellipsis we omit the that in order to keep the tone of the sentence casual and conversational.
Now the second clause of the sentence (I know the person you’re talking about) begins with its own transitive verb (know), and the object of that verb (the person) is followed by three words (you’re talking about) that make the noun person more definite: I don’t know just a person; I know the person you’re talking about. Any element that modifies a noun works as an adjective, so the three words you’re talking about comprise an adjectival clause connected to person. But connected how?
That clausal adjective makes up the third clause of the sentence, but it ends with a preposition (about) for which no object is named. One great master rule of English is that prepositions must have objects, so what is going on here? Another instance of ellipsis. This third clause, you’re talking about, has omitted its initial relative pronoun whom, which would and could (but not necessarily should) stand as the prepositional object. And I say not necessarily should, because omitting the relative pronoun keeps the tone of the sentence relaxed, just as omitting the conjunction that did a few words earlier. Recall the imagined context of the sentence (two friends in an everyday conversation) and you will quickly realize how unnaturally stiff a grammatically complete statement would have been in the living moment: I think that I know the person whom you’re talking about.
Being able to analyze a sentence is a way to keep ourselves alert—not just for material grammatical and logical errors, but also for matters of tone and style and affability. The living moment is all, some casual, some formal, some somewhere in between. We should aim at a lithe and facile language that is both meaningful and appropriate to the circumstance in which it arises.