Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas; how comes it to be furnished? Whence comes it by that vast store, which the busy and boundless fancy of man has painted on it, with an almost endless variety? Whence has it all the materials of reason and knowledge? To this I answer, in one word, from experience: in that, all our knowledge is founded; and from that it ultimately derives itself.

—John Locke, Essay Concerning Human Understanding

This passage is one of the most famous formulation of the tabula rasa account of the human mind. Tabula rasa is Latin for “blank slate,” which is the traditional metaphor used to explain the theory. At birth, the mind is like a blank chalk board, devoid of writing; our experience is the hand that writes upon us; and our knowledge is the end result.

John Locke held that there was nothing in the mind that did not originate in the senses. Yes, we could have abstract ideas, like our notion of a triangle; but these ideas were simply generalizations from individual triangles that we have experienced through our eyes. Thus all knowledge, however general, abstract, or theoretical, was just a summary of our experience.

In Locke’s own lifetime, this idea was contested by Leibniz, who wrote an entire book-length response to Locke’s Essay, arguing that the mind needed certain innate principles in order to acquire knowledge. And this puzzle—the respective roles of experience, sense data, induction, deduction, and abstraction in our knowledge of the world—forms the basis of Kant’s magnificent Critique of Pure Reason.

Locke was a philosopher, and thus his Essay is largely concerned with epistemology—the nature, limit, and acquisition of knowledge. Yet this debate—empiricism versus rationalism, the “blank slate” versus “innate ideas”—is often reframed, in today’s world, as a scientific controversy.

The most famous example of this that I’m aware of is the controversy in linguistics. How much structure must we posit in the human brain in order to account for language acquisition? These classic answer to this question was given by Chomsky. He argued that, contrary to Locke, we can’t imagine the brain at birth as a blank slate, but must assume an enormous amount of complex machinery.

Several arguments led him to this conclusion, the most famous of which was the “poverty of input.” This is the observation that, without some kinds of basic assumptions guiding their derivation, children are not exposed to nearly enough examples of language in order to derive the correct grammatical form. For the human infant trying to guess the meaning of an unknown sentence, there are an enormous number of logical possibilities. If the language learner had to eliminate each one of these possibilities one by one, then it would take far too much time. Thus some in-built, innate schema must allow them to guess intelligently.

Not only that, but for the learner attempting to divine the deep structure from the surface structure, they must contend with the fact that the surface structure of a language is often misleading. Consider these two sentences: (A) “I expected the doctor to examine John,” and (B) “I persuaded the doctor to examine John.” Now let’s say we transform the first sentence into the passive voice: “I expected John to be examined by the doctor.” Notice that the meaning of this sentence is identical with the earlier sentence.

Suppose the learner, reasoning by analogy, transformed sentence (B) the same way, resulting in “I persuaded John to be examined by the doctor.” Now notice that the meaning of this new sentence is different from the first one. In the active voice the doctor is being persuaded, and in the passive voice John is. And this, despite undergoing what, superficially at least, appears to be the same transformation as sentence (A). Clearly, there is more to the grammar than meets the eye.

From all this, Chomsky concludes that there must be a “Universal Grammar,” which is a schema in the brain that determines which types of grammatical rules are permissible. Put more simply, Universal Grammar is something that allows learners to guess intelligently, rather than randomly, about the structure of language. Clearly such a schema would be a lot of information to be born with. In this, Chomsky resembles Leibniz and Kant far more than Locke and Hume.

But you don’t really need any of Chomsky’s arguments to realize that there must be some innate organization in our brains that allow us to learn language. After all, almost every person learns a language, while dogs and cats, who also have brains, and who are exposed to about as much language, never pull it off. Computers are better at many cognitive tasks than humans; and yet a few minutes with Google Translate is enough to convince anyone that computers haven’t quite gotten the hang of language. Clearly there is something special about the human brain that allows us to acquire language, while cats and computers struggle.

Thus we are left with several interesting questions. First, how much information and organization does the human brain possess at birth? How much of this information consists of general learning strategies, and how much is specific to language acquisition? And what exactly does this information consist of? Chomsky’s model of Universal Grammar, for example, was an attempt to answer this last question, by proposing a set of conditions that all languages must abide by. But his model has of late been criticized, first, for positing too much organization, and second, for failing to account for the structure of certain rare languages.

I am not a linguist, and thus I cannot hope to solve this controversy, or even make an interesting contribution to it. I only want to point out that this debate, although new in form, harks all the way back to Plato and Aristotle. Plato thought all knowledge was buried in the mind, and all philosophers had to do was uncover it; and Aristotle, like Locke, thought that knowledge derived from the senses. It is obvious to everyone by now that either extreme must be wrong. But apparently 2,500 years hasn’t been enough time for us to come to a conclusion.

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