When we have a thought, we know what it is because of language; it's how we tell ourselves what the thought is. In its most basic definition, language gives us a way to understand ourselves and communicate with others.
When we have a thought, or hear the thoughts of others, we commonly think that language is an objective translator of things, and that if we hear someone (or even ourselves) correctly, the meaning is obvious. But in truth neither speaking nor hearing language is a neutral process.
Each time we "tune-in" to our own experience or hear what someone else is saying, we filter it through our own plethora of emotions, memories, thoughts, and experiences, giving it meaning oftentimes without even being aware that is what we are doing. This can often give rise to miscommunication and conflict wherein the words are heard accurately but the intended meaning is not received.
Over the last half a century researchers have been giving thought to a more subtle and difficult to define filter of language and meaning: the idea that the language we learn to think in (our "mother tongue") may actually help to shape the way we think. For example, some languages (such as English) use egocentric directions which depend on our own bodies, such as left, right, front and back. Other languages depend completely on geographic directions - north, south, east, and west - which do not rotate with the speaker wherever they turn. It is fascinating to imagine how this difference might this serve to give a person a different sense of themselves in relationship with the world around them - as central to direction versus oriented to the world around them.
Another example includes color: it turns out that the colors our language routinely obliges us to treat as distinct can refine our visual sensitivity to color differences in reality. Thus our brain is trained to exaggerate the distance between shades of color if these have different names in our language; differently then cultures who don't have names for the different shades. In yet another example, time and fact are understood differently. In English, if we believe something to be true we state it as fact, whereas in some cultures if it is not in front of them they cannot report it that way, even if they saw it five minutes ago. This gives the speaker a very different sense of what they can know to be true.
All of this means, then, that language is not just simply a way of expressing thoughts, feelings, ideas, perceptions, or memories. Language also informs those things. And since language development begins in infancy, our mother tongue also has an affect on the person we become.
This discussion could move from here into the debate regarding bilingual education and the importance of learning in ones' mother tongue versus the benefits of learning in another language. Both have been found to have benefits and drawbacks. Learning in the mother tongue promotes types of brain activity and acuity, and speaks to the learner in a deep, resonant level. Learning in a different language helps to open the door to other cultures, and can improve cognitive and linguistic abilities.
But regardless of which side of that debate you may land on, the evidence is becoming more and more clear: the language in which you think has an affect on the way that you think, how you relate to others, and, ultimately, the person you become. It also becomes clear that we need to be careful about making assumptions of meaning when communicating with others whose mother tongue is different than our own - we all might be speaking the same words but they do not always mean the same thing.
