Language acquisition

Language acquisition is the process by which humans acquire the capacity to perceive and comprehend language, as well as to produce and use words and sentences to communicate. Language acquisition is one of the quintessential human traits,because non-humans do not communicate by using language. Language acquisition usually refers to first-language acquisition, which studies infants' acquisition of their native language. This is distinguished from second-language acquisition, which deals with the acquisition (in both children and adults) of additional languages.
The capacity to successfully use language requires one to acquire a range of tools including phonology, morphology, syntax, semantics, and an extensive vocabulary. Language can be vocalized as in speech, or manual as in sign. Human language capacity is represented in the brain. Even though human language capacity is finite, one can say and understand an infinite number of sentences, which is based on a syntactic principle called recursion. Evidence suggests that every individual has three recursive mechanisms that allow sentences to go indeterminately.
 These three mechanisms are: relativization, complementation and coordination. 
 Furthermore, there are actually two main guiding principles in first-language acquisition, that is, speech perception always precedes speech production and the gradually evolving system by which a child learns a language is built up one step at a time, beginning with the distinction between individual phonemes.
 similarities in learning and learning:

• In both first and second language acquisition, universal grammar may influence learning.  In second language learning, universal grammar may influence learning either independently or through the first language.
• In both first and second language acquisition, there are predictable stages, and particular structures are acquired in a set order.  Individuals may move more slowly or quickly through these stages, but they cannot skip ahead.
• In both first and second language acquisition, making errors is a part of learning.  Learners need to make and test hypotheses about language to build an internal representation of the language.  In the initial stages of learning, learners may use chunks of language without breaking them down or processing them as independent units.  In later stages, they may make new errors as they begin to process the parts of each chunk according to the rules of their language system.  For example, a learner may start out using the correct form of an irregular verb as part of a language chunk, but later overgeneralize and place a regular affix on that same verb.
• In both first and second language acquisition, the learner uses context clues, prior knowledge, and interaction to comprehend language.
• In both first and second language acquisition, age is an important variable affecting proficiency. 
• In both first and second language acquisition, learners can often comprehend more complex language than they are able to produce.  In the initial stages of learning, learners go through a silent period. 
• In both first and second language acquisition, a learner's proficiency can vary across situations.
• In both first and second language acquisition, learners may overgeneralize vocabulary or rules, using them in contexts broader than those in which they should be used.
• In both first and second language acquisition, learners need comprehensible input and opportunities to learn language in context in order to increase their proficiency.

Differences:

• In first language acquisition, the basis for learning is universal grammar alone.  In second language acquisition, knowledge of the first language also serves as a basis for learning the second language.  There may be both positive and negative transfer between languages in second language learning.
• In first language acquisition, children spend several years listening to language, babbling, and using telegraphic speech before they can form sentences.  In second language acquisition in older learners, learning is more rapid and people are able to form sentences within a shorter period of time. 
• In formal second language learning in older learners, learners are able to use more metacognitive processes in their learning.  They can consciously analyze and manipulate grammatical structures, and they can explicitly describe how language works.  This can speed the learning process.
• In second language learning in older learners, learners bring more life experience and background knowledge to their learning.  They have more schemata and more learning strategies to help them learn the second language.
• In second language learning in older learners, there may be less access to universal grammar, and sensitivity to phonological distinctions not present in the native language will be reduced.  Students learning in a classroom setting may also have fewer opportunities to learn language authentically.  These factors may reduce the likelihood that second language learners will attain native-like proficiency.  First-language learners always attain native proficiency, unless they have a disability that affects language learning.
• In first language acquistion, learners have many chances to practice with native speakers (especially caregivers).  In second language acquisition, learners may or may not have the opportunity to practice extensively with native speakers.
• Almost everyone acquires a first language, but not everyone acquires a second language.  Acquiring a first language happens naturally, while acquiring a second language often requires conscious effort on the part of the learner.