<b>Language acquisition</b> is the process by which humans acquire the capacity to perceive and comprehend <a title="Language" href="https://en.wikipedia.org/wiki/Language">language</a>, as well as to produce and use <a title="Word" href="https://en.wikipedia.org/wiki/Word">words</a> and <a title="Sentence (linguistics)" href="https://en.wikipedia.org/wiki/Sentence_(linguistics)">sentences</a> to communicate. Language acquisition is one of the quintessential human traits, because <a title="Animal language" href="https://en.wikipedia.org/wiki/Animal_language">non-humans do not communicate by using language</a>. Language acquisition usually refers to <b>first-language acquisition</b>, which studies infants' acquisition of their <a title="First language" href="https://en.wikipedia.org/wiki/First_language">native language</a>. This is distinguished from <i><a title="Second-language acquisition" href="https://en.wikipedia.org/wiki/Second-language_acquisition">second-language acquisition</a></i>, which deals with the acquisition (in both <a title="Language acquisition by deaf children" href="https://en.wikipedia.org/wiki/Language_acquisition_by_deaf_children">children</a> and adults) of additional languages. The capacity to successfully use language requires one to acquire a range of tools including <a title="Phonology" href="https://en.wikipedia.org/wiki/Phonology">phonology</a>, <a title="Morphology (linguistics)" href="https://en.wikipedia.org/wiki/Morphology_(linguistics)">morphology</a>, <a title="Syntax" href="https://en.wikipedia.org/wiki/Syntax">syntax</a>, <a title="Semantics" href="https://en.wikipedia.org/wiki/Semantics">semantics</a>, and an extensive <a title="Vocabulary" href="https://en.wikipedia.org/wiki/Vocabulary">vocabulary</a>. Language can be vocalized as in speech, or manual as in <a title="Sign language" href="https://en.wikipedia.org/wiki/Sign_language">sign</a>. 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 <a title="Recursion" href="https://en.wikipedia.org/wiki/Recursion">recursion</a>. Evidence suggests that every individual has three recursive mechanisms that allow sentences to go indeterminately. These three mechanisms are: <i>relativization</i>, <i>complementation</i> and <i>coordination</i>. Furthermore, there are actually two main guiding principles in first-language acquisition, that is, <a title="Speech perception" href="https://en.wikipedia.org/wiki/Speech_perception">speech perception</a> always precedes <a title="Speech production" href="https://en.wikipedia.org/wiki/Speech_production">speech production</a> 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 <a title="Phoneme" href="https://en.wikipedia.org/wiki/Phoneme">phonemes</a>. Text is available under the <a href="https://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License" rel="license">Creative Commons Attribution-ShareAlike License</a>; additional terms may apply. By using this site, you agree to the <a href="https://wikimediafoundation.org/wiki/Terms_of_Use">Terms of Use</a> and <a href="https://wikimediafoundation.org/wiki/Privacy_policy">Privacy Policy</a>. Wikipedia® is a registered trademark of the <a href="https://www.wikimediafoundation.org/">Wikimedia Foundation, Inc.</a>, a non-profit organization.