Language acquisition and vocabulary acquisition are governed by a number of factors. The development of vocabulary is also governed by factors in culture and psychology, and borrowing words form other languages depends on the proximity of the two language groups, the cogency of the new term, and other factors that have been studied and about which theorists have speculated. Language is a vital part of human life, and hundreds of different languages are in use in the world today. Yet much is not known about the origin of language, the way languages have developed, the relationships among certain languages, and even the manner of acquisition of language. Linguists have developed the idea of different families of language to show how certain existing languages developed from an earlier root, though whether all languages can at some point be traced back to a single Ur-language remains a controversial subject. Words are being borrowed from other languages without perhaps considering why certain words are borrowed and why borrowing does not take place with other words, a process that has been continuing throughout human history.
Certain of these factors are involved in any sort of language acquisition or vocabulary building. Snow and Shapira look at the question of why some second-language learners achieve greater proficiency than others under the same conditions and find that this has puzzled researcher for many years, with many explanations. They find that much of the early research on attitudes and motivation in language learning was aimed at providing empirical evidence for the role played by social-psychological variables in second-language acquisition.
Many theories of language acquisition have incorporated these ideas. One of the models of language acquisition cited by Snow and Shapira is that of Krashen, earlier introduced by Dulay and Burt. This is the idea of the Affective Filter, introduced as the "socio-affec...