The Language Instinct: How the Mind Creates Language (13 page)

But the device does not work.
Either
must be followed later in a sentence by
or
, no one says
Either the girl eats ice cream, then the girl eats candy
. Similarly,
if
requires
then
; no one says
If the girl eats ice cream, or the girl likes candy
. But to satisfy the desire of a word early in a sentence for some other word late in the sentence, the device has to remember the early word while it is churning out all the words in between. And that is the problem: a word-chain device is an amnesiac, remembering only which word list it has just chosen from, nothing earlier. By the time it reaches the
or/then
list, it has no means of remembering whether it said
if
or
either
way back at the beginning. From our vantage point, peering down at the entire road map, we can remember which choice the device made at the first fork in the road, but the device itself, creeping antlike from list to list, has no way of remembering.

Now, you might think it would be a simple matter to redesign the device so that it does not have to remember early choices at late points in the sentence. For example, one could join up
either
and
or
and all the possible word sequences in between into one giant sequence, and
if
and
then
and all the sequences in between as a second giant sequence, before returning to a third copy of the sequence—yielding a chain so long I have to print it sideways (“Chapter 4”). There is something immediately disturbing about this solution: there are three identical subnetworks. Clearly, whatever people can say between an
either
and an
or
, they can say between an
if
and a
then
, and also after the
or
or the
then
. But this ability should come naturally out of the design of whatever the device is in people’s heads that allows them to speak. It shouldn’t depend on the designer’s carefully writing down three identical sets of instructions (or, more plausibly, on the child’s having to learn the structure of the English sentence three different times, once between
if
and
then
, once between
either
and
or
, and once after a
then
or an
or
).

But Chomsky showed that the problem is even deeper. Each of these sentences can be embedded in any of the others, including itself:

For the first sentence, the device has to remember
if
and
either
so that it can continue later with
or
and
then
, in that order. For the second sentence, it has to remember
either
and
if
so that it can complete the sentence with
then
and
or
. And so on. Since there’s no limit in principle to the number of
if
’s and
either
’s that can begin a sentence, each requiring its own order of
then
’s and
or
’s to complete it, it does no good to spell out each memory sequence as its own chain of lists; you’d need an infinite number of chains, which won’t fit inside a finite brain.

This argument may strike you as scholastic. No real person ever begins a sentence with
Either either if either if if
, so who cares whether a putative model of that person can complete it with
then…then…or…then…or…or?
But Chomsky was just adopting the esthetic of the mathematician, using the interaction between
either-or
and
if-then
as the simplest possible example of a property of language—its use of “long-distance dependencies” between an early word and a later one—to prove mathematically that word-chain devices cannot handle these dependencies.

The dependencies, in fact, abound in languages, and mere mortals use them all the time, over long distances, often handling several at once—just what a word-chain device cannot do. For example, there is an old grammarian’s saw about how a sentence can end in five prepositions. Daddy trudges upstairs to Junior’s bedroom to read him a bedtime story. Junior spots the book, scowls, and asks, “Daddy, what did you bring that book that I don’t want to be read to out of up for?” By the point at which he utters
read
, Junior has committed himself to holding four dependencies in mind:
to be read
demands
to, that book that
requires
out of, bring
requires
up
, and
what
requires
for
. An even better, real-life example comes from a letter to
TV Guide:

At the point just after the word
not
, the letter-writer had to keep four grammatical commitments in mind: (1)
not
requires -
ing
(her anger at
not
receiv
ing
acclaim); (2)
at
requires some kind of noun or gerund (her anger
at
not
receiving acclaim
); (3) the singular subject
Pam Dawber’s anger
requires the verb fourteen words downstream to agree with it in number (Dawber’s
anger…derives
from); (4) the singular subject beginning with
How
requires the verb twenty-seven words downstream to agree with it in number (
How…escapes
me). Similarly, a reader must keep these dependencies in mind while interpreting the sentence. Now, technically speaking, one could rig up a word-chain model to handle even these sentences, as long as there is some actual limit on the number of dependencies that the speaker need keep in mind (four, say). But the degree of redundancy in the device would be absurd; for each of the thousands of
combinations
of dependencies, an identical chain must be duplicated inside the device. In trying to fit such a superchain in a person’s memory, one quickly runs out of brain.

The difference between the artificial combinatorial system we see in word-chain devices and the natural one we see in the human brain is summed up in a line from the Joyce Kilmer poem: “Only God can make a tree.” A sentence is not a chain but a tree. In a human grammar, words are grouped into phrases, like twigs joined in a branch. The phrase is given a name—a mental symbol—and little phrases can be joined into bigger ones.

Take the sentence
The happy boy eats ice cream
. It begins with three words that hang together as a unit, the noun phrase
the happy boy
. In English a noun phrase (NP) is composed of a noun (N), sometimes preceded by an article or “determinator” (abbreviated “det”) and any number of adjectives (A). All this can be captured in a rule that defines what English noun phrases look like in general. In the standard notation of linguistics, an arrow means “consists of,” parentheses mean “optional,” and an asterisk means “as many of them as you want,” but I provide the rule just to show that all of its information can be captured precisely in a few symbols; you can ignore the notation and just look at the translation into ordinary words below it:

The rule defines an upside-down tree branch:

Here are two other rules, one defining the English sentence (S), the other defining the predicate or verb phrase (VP); both use the NP symbol as an ingredient: