In studying grammar, it can be helpful—or inspiring or consoling even—to remember the difference between complex and complicated. When we say something is complex, we mean that it has many different parts, all working smoothly together as an intricate system. When we say that something is complicated, though, we mean that it has many different parts, but we can’t see how they all work together and we’re not really sure they even do. Something that is complex can be beautiful; something complicated, never.
All of the pieces of grammar, what are called the parts of speech, are more complex than they are complicated, for they do largely work together successfully as a system. But that cooperative complexity can be a challenge at times to see. How, for example, are we to understand the two instances of the word what in this simple exchange between two friends: What more do you want? I told you what he said. The parts of speech help us classify how a word can be used grammatically, and in both instances here, the word what is a pronoun, a word that is being substituted for another word, usually a noun or an element being used as a noun. But to say that what is a pronoun doesn’t answer much because there are, by some reckonings, eleven different ways a pronoun can be used. Complexity, indeed.
The first sentence is posing a question, and we know that because the verb do, auxiliary to the verb want, stands before the subject of the sentence; subjects usually precede their verbs, and so the inversion here signals that a question is being asked. As the first word of an interrogative statement, the word what confirms the question, and so we can be sure that this instance of the word what can be explained as an interrogative pronoun, one of those eleven uses of a pronoun. And we can appreciate the intricacy one step more by understanding that this interrogative pronoun is presenting itself as the direct object of the transitive verb want, which we can see if we unwind the word order back into its declarative form: you want what.
Now the second sentence wants us to sharpen our sword. The first observation to make in analyzing the sentence I told you what he said is that the statement is made up of two clauses, I told you and what he said. We can dispose of the first clause easily enough: I is the subject of the transitive verb told, and you is its indirect object. Transitive verbs, as we know, have direct objects, so if we ask what it is that was told, we would have to answer with the entire second clause: what he said. This second clause, then, is in its entirety the direct object of the transitive verb told. But how does it work in its own right and how is it connected to the first clause?
This second clause begins with the word what, but unlike the first sentence we examined, what is not here an interrogative pronoun but a relative pronoun, and what is called a compound, or double, relative, to boot. All relative pronouns connect clauses in a sentence by substituting in their own clause a word that refers to a noun in another clause, the identification bringing the two clauses into relationship; we do this all the time in sentences like the film that I saw last night was fantastic, where the relative pronoun that refers in its own clause (that I saw last night) to the noun film in the main clause (the film was fantastic). That identity of meaning but difference of grammatical use fuses the two clauses into one meaning.
A compound relative pronoun, though, brings an interesting twist to this configuration. The word what in the second clause really means that which, and when we unpack the word like this, we can see that it is made up of the demonstrative pronoun that (yet another of those eleven uses of a pronoun) together with the simple relative pronoun which in reference to it. So to say what he said is really to say that which he said; that is the object of the transitive verb told in the first clause, and which is the relative pronoun referring to that, which in turn is the object of the transitive verb said in the second clause. The double relative double weaves the syntax between the two clauses, producing a tight, sure, brief statement. All of which makes it strange but true to say that grammatical complexity can be at times a way to concision, one of the high achievements of good writing.