A new study suggests that language may rely less on complex grammar than previously thought.
Every time we speak, we’re improvising.
“Humans possess a remarkable ability to talk about almost anything, sometimes putting words together into never-before-spoken or -written sentences,” said Morten H. Christiansen, the William R. Kenan, Jr. Professor of Psychology in the College of Arts and Sciences.
According to language scientists, this flexibility comes from internal mental representations that help people recognize patterns in language and combine words into meaningful statements. While this ability is fundamental to communication, scientists are still working to understand exactly what those mental patterns look like and how they function, Christiansen said.
In a new study, Christiansen and co-author Yngwie A. Nielsen of Aarhus University present a different way of thinking about how language is represented in the mind. Their work questions the long-held belief that language depends on highly complex grammatical structures. Although the research focused on English, the authors suggest the results may apply to many languages and could influence future research on how language evolves, how children learn to speak, and how adults acquire new languages.
From Grammatical Trees to LEGO-Like Building Blocks
For many years, researchers have assumed that sentence construction depends on an internal grammar that organizes words into layered, hierarchical structures, similar to a branching tree. Christiansen and Nielsen propose a simpler alternative. They suggest that language may rely more on combining familiar building blocks, much like assembling pre-made LEGO pieces (such as a door frame or a wheel set) into a finished structure.
Under this view, speakers draw on short, linear sequences of word types, including nouns and verbs, rather than relying entirely on abstract grammatical rules. Some of these sequences do not fit neatly into traditional grammar at all, such as “in the middle of the” or “wondered if you.”
Their study was published in the journal Nature Human Behaviour on January 21.
Since at least the 1950s, the dominant theory in linguistics has emphasized hierarchical mental structures as a defining feature of human language, Christiansen said. This framework suggests that words and phrases are combined according to grammatical principles into larger units known as constituents. For instance, in the sentence “She ate the cake,” the words “the” and “cake” form the noun phrase “the cake”. That phrase then joins with “ate” to create the verb phrase “ate the cake,” which finally combines with “she” to form a complete sentence.
“But not all sequences of words form constituents,” Christiansen and Nielsen wrote in a summary of their paper. “In fact, the most common three- or four-word sequences in language are often nonconstituents, such as ‘can I have a’ or ‘it was in the.’”
The Hidden Role of Nonconstituent Sequences
Because they don’t conform to grammar, nonconstituent sequences have been overlooked. But they do play a role in a speaker’s knowledge of their language, the researchers found.
In experiments, an eye-tracking study and an analysis of phone conversations, they discovered that linear sequences of word classes can be “primed,” meaning when we hear or read them once, we process them faster the next time. That’s compelling evidence they’re part of our mental representation of language, Christiansen said. In other words, they’re a key part of our mental representation of language that goes beyond the rules of grammar.
“I think the main contribution is showing that traditional rules of grammar cannot capture all of the mental representations of language structure,” Nielsen said.
“It might even be possible to account for how we use language in general with flatter structure,” Christiansen said. “Importantly, if you don’t need the more complex machinery of hierarchical syntax, then this could mean that the gulf between human language and other animal communication systems is much smaller than previously thought.”
Reference: “Evidence for the representation of non-hierarchical structures in language” by Yngwie A. Nielsen, and Morten H. Christiansen, 21 January 2026, Nature Human Behaviour.
DOI: 10.1038/s41562-025-02387-z
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