We live in a world where bilingualism is no longer exceptional. Estimates suggest that more than half of the world’s population uses two or more languages (or dialects) in everyday life. Yet for something so common, the term bilingual is surprisingly slippery.
Is a bilingual someone who grew up with two languages? Someone who learnt English at secondary school but now uses it on a daily basis? Someone who speaks fluently but still avoids writing emails? In classrooms, research & placement decisions, the term often functions more like a label than a measurement.
A recent study by Chen & Blanco-Elorrieta (2025) tackles this problem head-on by asking a simple but powerful (& dare I say ‘obvious’) question: what if bilingualism & language dominance were treated as continua, not categories?
The study
The researchers set out to create a clearer, more practical way of describing people’s language profiles. Instead of relying on long lists of background questions or vague self-descriptions, they proposed two simple scores:
- a language dominance score showing which language is stronger, or whether the person is fairly balanced
- a multilingualism score placing someone on a scale from monolingual to highly multilingual
Rather than using dozens of variables, the model focuses on just two:
- how proficient people feel they are in each language
- how old they were when they started learning each one
These scores were tested using data from over 250 people across two very different groups: younger adults & older bilinguals with language difficulties. The aim was to see whether a simple model could still reflect the complexity of real language lives.
For anyone curious, the researchers have also made an open-access online calculator, so you can try the model yourself.
The findings
The results were strikingly consistent:
- Self-ratings of proficiency closely matched formal language test results, suggesting that learners generally know their own strengths & weaknesses.
- Age of acquisition mattered, but mainly as part of a bigger picture, not as a rigid cut-off.
- The new, simple scores produced almost identical results to much more complex statistical models used in previous research.
In short, simplicity did not mean inaccuracy.
Why this matters for language teachers
This study fits with a growing body of research arguing that bilingualism is not an on/off switch but a gradient. That idea will feel familiar to anyone who has taught adult learners.
Two students may both be labelled “B2”, yet one speaks confidently but avoids writing, while the other reads complex texts but struggles in conversation. Calling both equally bilingual hides more than it reveals.
Thinking in terms of scales rather than boxes better reflects how languages actually live in people.
Teacher Takeaways?
- Treat learner language profiles as flexible & evolving rather than fixed categories.
- Trust learner self-assessment more than we sometimes do, especially when it is guided & structured.
- Be cautious with labels like dominant language or balanced bilingual unless you are clear what they actually mean.
Does this research what you’ve suspected all along?
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