Some people find it useful to talk through their problems — but cognitive neuroscientists at MIT's McGovern Institute for Brain Research assert that language isn't necessary for logical reasoning. Research led by MIT associate professor of brain and cognitive sciences Evelina Fedorenko shows that individuals can perform well on tasks requiring logical reasoning even when their language abilities are severely impaired. Moreover, brain imaging reveals that language-processing areas of the brain are not engaged in logical reasoning. Philosophers, linguists, and cognitive scientists have debated the relationship between language and thought for millennia, with many arguing that we use language to think. Hope Kean acknowledges a close relationship between logic and language, noting that abstract thinking has structural properties akin to language. However, she and Fedorenko suspected that while we largely depend on language to communicate logical reasoning, the brain may utilize a separate system for reasoning itself.
Logical reasoning demands precision that language often lacks, and language is linear, processing one word at a time, while evaluating information for logical conclusions may require less linear thinking. Kean's curiosity about how the brain handles logical reasoning led to a challenging scientific question, as it is difficult to exclude language when studying human participants. Fedorenko's team collaborated with neuroscientist Rosemary Varley from University College London, who studies acquired language disorders, to work with two patients who experienced strokes damaging language-processing areas of their brains, resulting in severe impairments in language comprehension and production. They designed language-free logic games where participants had to infer relationships between sets of numbers.
In a second game, participants were presented with geometric patterns and asked to identify another pattern to complete the matrix. As participants solved increasingly difficult puzzles, it became clear that people do not need language for this kind of reasoning. Patients with language impairments solved the problems as well as a control group and were even able to communicate the inferred rules using gestures or sketches. Kean remarked, "This really upends a theory that says symbolic rule induction is not possible without linguistic capacities."
Alongside this part of the study, Kean and colleagues used functional brain imaging to study brain activity in healthy adults during logical reasoning tasks. Participants underwent a series of MRI scans capturing their brain activity while completing various logic games. They also engaged in tasks designed to map the language-processing areas of their brains. Another set of tasks mapped each person's so-called "multiple demand network" — a distributed brain system that supports complex problem-solving. Neurotypical participants completed logic games similar to those used with language-impaired patients and were presented with problems requiring syllogistic reasoning. The team varied the difficulty of the logic puzzles to observe which brain areas became more active as logical reasoning intensified. Notably, the MRI scans showed that the brain's language system is not engaged for either inductive reasoning (when identifying hidden rules) or deductive reasoning (when assessing the validity of syllogistic conclusions). Surprisingly, the multiple demand network, suspected by many scientists to be important for logical reasoning, was engaged during inductive reasoning but did not seem to be involved in deductive reasoning — a finding Kean is building on in her ongoing work.
For Fedorenko and Kean, these findings strongly support the separation of logic and language in the brain. They add to previous findings from Fedorenko's lab showing that other types of thinking, such as object categorization and social reasoning, also do not rely on language. The researchers emphasize the implications for understanding acquired language impairments, or aphasia. Specialists have long recognized that loss of language does not equate to loss of intelligence. People with aphasia can still enjoy chess, solve sudoku puzzles, or manage family finances. Fedorenko states, "This research adds to a growing body of work establishing that even severely aphasic individuals can preserve their ability for abstract logical thought — a defining feature of our species."
There could be implications for artificial intelligence too. Large language models like ChatGPT and Claude are trained entirely on text and use text as their output — yet they convincingly simulate some kinds of human reasoning. Exploring the differences between these models and the human brain, where language and abstract logical thought are distinct, might offer useful insights to inform future models, Kean says. When it comes to understanding how the human brain reasons, Kean calls this a new frontier in the geography of thought — and she is eager to explore it.
Blogger's Review: This study challenges conventional beliefs, indicating that logical reasoning and language are not inseparable, revealing the complexity and diversity of human thought. The research on aphasia not only offers a new perspective for psychology but may also have profound implications for the development of artificial intelligence. Understanding the relationship between thought and language helps us better define the essence of intelligence.