word1.Introduction:describing and explaining L2 acquisitiona.What is Second language acquisition?Its emergence is no accident. This has been a time of the global village and the World wide Web. As never before ,people have had to learn a second language ,not just as a pleasing pastime ,but often as a means of obtaining an education of securing employment.Second can refer to any language that is learned subsequent to the mother tongue. It can refer to the third or fourth language.Also, second is not intended to contrast with foreign. so L2 acquisition can be defined as the way in which people learn a language other than their mother tongue ,inside or outside of a classroom.Second Language Acquisition is the study of L2 acquisition.b.What are the goal of SLA?Some approaches for you to set about finding how the learners acquire an L2:1.ask the learners how they did it .This approach has provided some valuable insights but it is limited in that learners are not aware of the actual learning process they engaged in2.collecting samples of learner language that learners produce and analyse them carefully .These samples provide evidence of what the learners know about the target language .If the samples are collected at different points in time ,It may be possible to find out how learners knowledge gradually develops. in other words , what we are trying to is describe how learner language change over time.c.the focus of SLASLA has not focused on these municative aspects of language development - how learners overall ability to municate develops, how they bee more fluent in their use of an L2 .but on the formal features of language that linguists have traditionally concentrated on .- pronunciation (how learnersaccents change over time.) words-how learners build up their vocabulary；most of ten ,the focus has been on the grammar-the focus has been the grammar of the L2d.the goals of SLAOne of the goal of SLA is the description of L2 acquisition.Another is explanation; identifying the external and internal factors that account for why learners acquire an L2 in the way they do. One of the goal of SLA are to describe how L2 acquisition proceeds and to explain this process and why some learners seem to be better as it than others.e.What are the external and internal factors?One of the external factors is the social milieu in which learning takes place. Social conditions influence the opportunities learners have to hear and speak the language and the attitudes that they develop towards it.Another external factor is the input that learners receive,that is,the sample of language to which a learner is exposed. Language learning can not occur without some input.L2 acquisition can be explained in part by these external but internal factors also should be considered. Learner possess cognitive mechanisms which enable to extract informationabout L2 from the input.L2 learner bring an enormous amount of knowledge to the task of learning an L2.First,they can draw on the mother tongue ,Second, learners possess general knowledge about which can help them understand L2 input .Finally ,learners possess munication strategies that help them make effective use of their L2 knowledge. Besides ,it has been suggested that people vary in their language aptitudef.two case studiesA case study is a detailed study of a learners acquisition of an L2,which is longitudinal, involving the collection of samples of the learners speech or writing over a period of time. One is of an adult learner learning English in surroundings where it serves as a means of daily munication and the other of two children learning English in a classroom.Research Schmidt says-.Wes ,a naturalistic learner -who learns English by learning to municate in it; he was still far short for native speaker accuracy, but he did develop in other ways, eg, his use of formula, he can identify the fixed phrases and practise them consciously. This help him develop fluency in English, In fact , we is a successful municator, a skilled conversationalist.Researcher Rod Ellis says-J and R .the instruction the two learners received involves both formal instruction and informal instruction. The focus is the request. because English is the medium of munication ,there are numerous opportunities for them to hear and perform requests. the similarities between J and R ;1,both were capable of successfully performing simple requests.2,both manifested development in their ability to perform requests.3.many of their requests seemed formulaic in nature.4,both progressed in much the same way despite the fact they had different native languages, however ,the ability is limited in a number of respects.5,in short ,despite ample opportunity to master requests, both were still far short of native like petence at the end of the study.P11.Methodological issues1,what needs to be described2,what it means to say that a learner has acquired a feature of the target language.(Schmidt defines acq