Summary: Toddlers as young as 19 months demonstrate an early capacity for logical thought that operates independently of spoken language. This ability, often expressed as reasoning by exclusion, lets infants draw conclusions about unfamiliar situations by eliminating options they recognize as impossible.
By tracking where infants look during carefully designed tests, researchers identified patterns consistent with this innate reasoning. The study also found no meaningful difference between bilingual and monolingual toddlers, indicating that this form of early logic does not depend on specific language experience.
Key facts:
- Toddlers from at least 19 months of age display logical reasoning that does not rely on fully developed language skills.
- The dominant strategy observed is exclusion by elimination—ruling out known alternatives to infer the unknown.
- The study found no significant differences between bilingual and monolingual infants, supporting the view that this reasoning is a general feature of early cognition.
Source: UPF Barcelona
How do children learn to speak and build knowledge about the world? Social interaction in the family and educational settings plays a major role, but these factors are not the whole story.
New research from the Center for Brain and Cognition at Pompeu Fabra University (UPF) shows that a form of natural logical thinking emerges very early and supports learning independently of language. The study, published in Current Biology, indicates that infants use deductive strategies—particularly exclusion by elimination—to reduce uncertainty and map words to objects or to infer hidden information.
The research tackles a debated question in neuroscience: can infants who have not yet mastered speech nonetheless engage in logical reasoning? The findings document that by 19 months, infants reliably use logical processes to handle ambiguous situations, often preferring elimination of impossible options over simple associative guessing.
Put simply, when confronted with something unknown, toddlers tend to analyze the situation and infer conclusions by ruling out options they already recognize as incorrect, according to their current knowledge.
The study, titled The scope and role of deduction in infant cognition, is authored by Kinga Anna Bohus, Nicolo Cesana-Arlotti, Ana Martín-Salguero and Luca Lorenzo Bonatti. L. Bonatti (ICREA) leads the Reasoning and Infant Cognition (RICO) research group at UPF’s Center for Brain and Cognition; Kinga Anna Bohus is the main author. N. Cesana-Arlotti and Ana Martín-Salguero, formerly affiliated with UPF, are now researchers at Yale University and the École Normale Supérieure in Paris, respectively.
Toddlers resolve uncertainty by ruling out impossible options based on their current knowledge
The study contrasts two strategies infants might use when faced with ambiguous information: association and exclusion. Association involves forming a tentative link between a new word and several possible objects, favoring the one that seems to fit best. Exclusion, by contrast, involves actively eliminating known alternatives to identify the referent of a novel term. The evidence shows that exclusion is the predominant approach.
For example, if a toddler sees objects A and B and hears a novel word that they know does not refer to A (because they already know A’s name), they infer that the new word must name B. This elimination strategy allows infants to deduce meanings and make reliable choices even with limited language.
Two experiments tested infants’ reasoning with familiar and unfamiliar objects and words
Researchers ran two experiments. The first involved 61 infants aged 19 months (26 monolingual, 35 bilingual); the second included 33 infants (19 monolingual, 14 bilingual). Comparing these groups helped determine whether deduction depended on language experience.
In the first experiment, infants saw pairs of objects and heard words while their eye movements were tracked. One test presented two familiar items (for example, a spoon and a biscuit) and asked infants to map a heard word to one of them. Another test paired a familiar object (an apple) with an unfamiliar one (for instance, a mechanical part), and the word heard either matched the familiar item or the unfamiliar item, allowing researchers to observe whether infants used association or exclusion.
The second experiment used object–sound associations. Two objects or figures were each linked to a distinct sound; the items were then hidden and one placed inside a container out of sight. When the objects were revealed, infants could see only one and had to infer by elimination which item was inside. In a follow-up task, a sound corresponding to one object was played to see if infants would look toward the correct, previously associated object.
Across tasks, researchers analyzed gaze patterns. When infants reasoned by exclusion, they frequently inspected one object, dismissed it as the referent, and then shifted their gaze to the other—an ocular “double-check” that signals disjunctive reasoning.
No meaningful differences between monolingual and bilingual infants
Kinga Anna Bohus summarizes the results: at 19 months, both bilingual and monolingual infants exhibit oculomotor patterns characteristic of disjunctive reasoning that have been observed in older children and adults. In other words, the emergence of logical inference at this age does not appear to depend on specific language experience.
While the study establishes the presence of this reasoning by 19 months, it remains an open question whether similar logical computations appear even earlier; additional research will be needed to trace the full developmental timeline.
About this neurodevelopment study
Author: Gerard Vall-llovera Calmet
Source: UPF Barcelona
Contact: Gerard Vall-llovera Calmet – UPF Barcelona
Image: Image credited to Neuroscience News
Original research: Closed access. “The scope and role of deduction in infant cognition” by Kinga Anna Bohus et al., published in Current Biology. DOI: 10.1016/j.cub.2023.08.028
Abstract
The scope and role of deduction in infant cognition
Highlights
- Markers of logical inference appear when 19-month-olds map novel words to referents.
- These markers also occur with familiar words and objects, indicating a broad use of logical strategies.
- Infants use inference by elimination in tasks that require identifying objects or locations.
- Early logical computations help reduce uncertainty and support learning about the world and language.
Summary
The origins of logically structured thought in humans remain debated. Studies of very young children produce mixed results: infants can generate and evaluate competing hypotheses, suggesting a structured “language of thought,” yet they sometimes fail tasks that seem to require similar representations. Disjunction—the notion that something is one thing or another—and disjunctive elimination—ruling out alternatives—provide a critical test for early logic.
This research documents the widespread presence of disjunctive reasoning in 19-month-old infants. In word–referent tasks, both bilingual and monolingual infants show oculomotor patterns that are hallmarks of disjunctive reasoning. The same reasoning appears in non-linguistic object-location tasks, demonstrating that infants spontaneously reason by elimination. Together, these findings suggest that early logical computations help organize knowledge by boosting confidence in some possibilities while eliminating others, thereby scaffolding learning about objects, language, and their relations.