A first language is the mother tongue or native language of a person while a second language is a language a person learns in order to communicate with the native speaker of that language.
The first language is like an instinct that is triggered by birth and developed with the experience of being exposed to it. A second language is a personal choice of a person.
There is no other alternative to a first language. A person cannot decide his/her first language. It comes to him/her as an inheritance/legacy/birthright. On the other hand, a second language is always fixed by the person. There are many alternatives to a second language. A person/community can choose a second language among other languages.
The acquiring process of the first language is very rapid while the learning process of the second language can vary from language to language and from person to person, but can never be as rapid as the first language acquisition.
The first language is ‘acquired’ and the second language is ‘learned’. The difference between these two words describes the qualities of the two languages. ‘Acquire’ means “to come into possession or ownership of” which indicates that the first language is like a dynamic and abstract property that comes into possession of a person. On the other hand, ‘learn’ means “to gain knowledge or skill by study, instruction, or experience” which indicates that there is nothing passive in second language learning.
A first language is completely acquired with 100% proficiency within 6 years from birth. However, a second language can never be learned as efficiently as a first language; though good competence can be achieved in the second language, the process is slow.
The first language acquisition is always natural and there is no need for instruction in acquiring it. But a second language learning is not natural and it needs continuous guidance and instruction.
The first language acquisition begins with telegraphic speech. The term ‘telegraphic speech’ deriving from the word ‘telegram’ was coined by Roger Brown, an American psycholinguist, in 1963. It refers to the two-word a child can utter when s/he is 18 to 24 months of age. Examples of telegraphic speech: Mom see, Dad go, No ball, Daddy walk, Mommy milk, etc. On the other hand, the second language acquisition begins with a full sentence. A child cannot start learning the second language without being fully efficient in the first language.
The first language is a natural part of a person’s everyday life. But the second language is a new aspect of the person’s life if s/he chooses it to be.
The first language does not require any conscious effort; the acquisition process of the first language is subconscious. The second language requires constant conscious effort so that the learners can internalize the structures of the second language