How do we humans end up using language in a way that conforms to grammatical rules? Recent research, using artificially designed languages, has disproved what many scientists used to think, that grammar and sentence order was learnt purely from habit: by listening to the way others speak.

The research shows the different grammatical patterns found in languages across the world are not just a result of centuries of linguistic and cultural interaction between peoples. They also involve deep principles in the human mind that drive how our brains represent language. Underneath all the linguistic differences, we are fundamentally alike.

Take a very simple example: what is it about English speakers that makes them say “Those three green balls”, while speakers of Thai end up saying the equivalent of “Balls green three those”? There’s a very simple and commonsense answer to this: when we learn our language, we learn that words like “those” are very often pronounced before words like “three”, not after them; that words like “three” are usually pronounced before words like “green”, and so on.

We learn this because we hear other people using language in this way, and we conform to the habits of the people around us. In this picture, grammar really is just a set of habits, or rules of behaviour.

In the recent study, Jennifer Culbertson and David Adger have shown this “commonsense” view cannot be the whole story. Instead, language learners assume there is an invisible structure to what they hear that is far more important than just the habitual ordering of words. This structure exists in the brain independently of what people learn and hear throughout life.

How was language learning tested?

The researchers’ experiments exposed English speakers to an artificially designed language, which uses English words, but which is like Thai in its word order. While in the English phrase “Those balls” the noun “balls” comes last, in the artificial language the noun “balls” instead comes first and is followed by words like “green”, “three” and “those”.

The people taking part in the experiments were asked, having heard many examples of this artificial language, to translate new examples from English into the made-up language. However, although the people learning the artificial language could tell from examples they heard that the noun comes first, they had no evidence about the order of the other words. That is, they just heard examples like “balls three”, or “cups green”. But that’s not enough to get the rule for what the order of “three” and “green” is: it could be like English (three green) or like Thai (green three).

The learners had to guess what the rules for these other cases were. Researchers then tested them to see how they had guessed.

This way of setting things up allowed the researchers to test whether the learners were applying their usual habits to the new language. The commonsense picture would predict that the learners, having been presented with examples that show the noun comes first, should just continue with their usual habits learned from English: words like “those” come before words like “three” which come before words like “green”. So that view predicts that the learners’ translations of more complex examples should follow the English order, but with the noun first (for example “balls those three green”).

What did researchers find?

This was exactly the opposite of what the researchers found. Instead, the learners translated the more complex examples along the pattern of Thai (“Balls green three those”), showing that the idea that a grammar of a language is just habits about ordering the words can’t be right. Instead, the researchers concluded that there are unconscious principles that organise the words of language. According to these principles, English and Thai are actually very similar, even though on the surface they seem directly opposite.

The researchers proposed an unconscious bias in our minds that leads to words like “green” coming closer to the noun than words like “three”, which come closer to the noun than words like “those”. Of course this principle is true of both the English and the Thai orders. It is not, however, true of the pattern that the “commonsense” story predicts (“balls those three green”), since “green” is very far away from the noun “balls”.

What’s yet more interesting about this idea is that linguists have found, looking at hundreds of different kinds of languages, that the Thai and English patterns are very common. The pattern that looks just like the order of English, but with the noun coming first, is much rarer, found mainly in some African languages like Kikuyu. So the English speakers in the experiment were behaving in a way that mimics how common the different patterns are across hundreds of languages.

This shows the different grammatical structures found in languages of the world are more a reflection of the deep properties of human minds than of social and cultural factors.