First languages are typically acquired without any conscious effort. As long as some form of language is capable of being heard, children will begin to process the noise, breaking it into individual sounds and eventually attempting to imitate those sounds. Eventually, they begin forming entire words, then basic strings of words, adding in affixes as they acquire the rules that govern them. Later in life, children may have to learn to use certain rules, which involves actual instruction, however typically they have some sort of underlying knowledge of how their language works.
Many of the theories on second language acquisition are based upon theories already in place for first language acquisition. However, acquiring a second language is different from acquiring one's first language. Many of the factors that we consider in looking at S.L.A. don't come into play when looking at F.L.A. including but not limited to age, necessity, personal characteristics, and outside factors. There is still much debate as to how second language is acquired or learned. The next pages will outline some of the theories, their strengths, and their weaknesses.