People differ in the extent to which they possess a natural ability for learning an L2. This ability, known as language aptitude, is believed to be partially related to general intelligence but also to be in part distinct. Language aptitude is thought to be a combination of various abilities, such as the ability to identify sound patterns in a new language, the ability to recognize the different grammatical functions of words in sentences, and the ability to infer language rules, and so on. It has been generally accepted that learners who achieve high scores in language aptitude tests learn rapidly and achieve high proficiency in second language learning. Yet how the components work on the learner’s inter-language development still remains speculative.