I have been thinking about this question for a long time.
The more languages I learn, teach and use, the less satisfied I am with the simple idea that your mother tongue is simply the first language you learned.
It is certainly the language that came first for most people.
But I think something else makes it different.
Your mother tongue is usually the language that was present while you were becoming the person you are.
You did not first become a fully formed person and then learn your mother tongue.
The two processes happened together.
You were learning words while discovering the world.
You were learning how to describe things while learning what those things meant to you.
You were learning how to communicate while developing relationships, experiencing emotions, forming memories and discovering your place among other people.
The language was there while all of this was happening.
That matters.
There is an interesting connection here with the word “native”.
It comes from the Latin nativus, related to nasci, meaning “to be born”.
That origin points towards something important: the idea of being native to a language is connected not simply with how well you speak it, but with where and how your relationship with that language began.
When you learn another language as an adult, the situation is fundamentally different.
You already have a history.
You already have memories.
You already have concepts, preferences, opinions, relationships, ambitions and an understanding of who you are.
You don’t learn the new language in order to construct that world from the beginning.
You bring an existing world into the new language.
This is one reason I have never been completely comfortable with the idea that adults should simply “learn a language like a child.”
The child is not merely learning another communication system.
The child is developing language while simultaneously developing a relationship with the world and with themselves.
An adult learning a new language is doing something different.
That does not mean adults cannot become extraordinarily proficient.
They can.
A later-learned language can become deeply familiar. It can become automatic. It can become the language of your professional life, your friendships, your relationships and your daily existence.
It can accumulate years and decades of personal experience.
But it arrived at a different point in your life.
It entered a person who already existed.
I became particularly aware of this after living abroad for many years.
When I first moved abroad, I could think about language largely as a practical question: Can I communicate? Can I understand people? Can I function?
After many years, the question became much more interesting.
What happens when the language in which you conduct much of your adult life is not the language through which you originally experienced childhood?
There are things that happen in one language that don’t necessarily happen in another.
A word can have a dictionary meaning, but it can also carry memories.
A language can contain not only vocabulary and grammar, but places, people, experiences, relationships and periods of your life.
That is why I think “mother tongue” describes something more than linguistic priority.
It describes a particular kind of relationship between language and biography.
This does not mean that a later language is somehow less real.
Nor does it mean that someone cannot develop an extremely deep relationship with a language learned later in life.
They can.
But there is one thing that cannot be recreated:
the experience of becoming a person through that language.
And perhaps this is one reason why language learning has interested me for so many years.
After more than 25 years of teaching and learning languages, I have become increasingly interested not only in how well someone knows a language, but in what kind of relationship they have with it.
Because knowing a language and having lived through a language are not necessarily the same thing.
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