Language is a combination of symbols that one user uses to place thoughts in the mind of another user of that language. If asked, why do you use language? Your answer would be as simple as, you speak because you desire to communicate. Surely, your answer would be true but the in depth of this would be that we speak because we want to convey our "thoughts".
This is where the brain enters. The human mind/brain is perhaps the most complex object in the universe, and we barely begin to comprehend the ways it is constituted and functions. Within it, language seems to occupy a central and a complex place.
Seldom, you may have wondered at your capacity to form phrases or sentences, speak smoothly or simply say what is on your mind. Still, you perhaps never gave much thought to why you have these abilities.
Let's take an example of a child who learns to speak and keenly absorbs signals from its environment. A child begins to speak by trying to repeat what he has heard his parents say. Have you ever heard a child say: "Daddy go, he hitted, no eat." These are not phrases he heard from his parents but in fact the child has chosen a two-word combination to express his thoughts and feelings.
So the question arises, how do we actually learn to speak effectively? Although hitted in the above example is not a word the child had heard from his adults. In other words, the only way a child learning language could make such an error is that he or she is learning a rule of the language. What the child hasn't mastered at this stage is the exceptions to the rule.
The evidence then indicates that children do, in fact, absorb a massive number of sentences and phrases but rather than mimic them back, they create their own grammar which they then apply to create new phrases never heard before. .
Although this is not conclusive but all of it suggests that language is an innate capacity of human beings which is acquired during a critical period between 2 to 7.