Language and interlanguage
Language can be thought of as a communication system of a specifically human type that conveys meaning by a medium such as sound. It consists of at least six interdependent subsystems: PHONOLOGY, the speech sounds and rules governing them; MORPHOLOGY, the inflection and derivation of words; SYNTAX, the principles of word order and of phrase and sentence construction; the LEXICON or vocabulary; SEMANTICS, word and sentence meaning; and PRAGMATICS, the background sociocultural conventions for adapting the output of the other components appropriately to the context or situation. For many languages, there is also an ORTHOGRAPHY, an alternative output system using written marks instead of sound.
The past century has witnessed a variety of proposals as to how these components function. The model shown in figure 0.1 synthesizes many of these proposals, showing (with arrows) their interaction with each other as we use them to speak, read, write, and listen. It greatly oversimplifies by omitting many internal mechanisms, by glossing over issues that have been controversial, and by neglecting the multitude of links to other kinds of human knowledge and behavior, but it should suffice for our purposes in this book.
Ordinarily, we treat a given language as a general system shared by all members of its speech community; otherwise, notions such as "Spanish language" or "Spanish-speaking" make no sense. Yet the system is not homogeneous; each component (e.g., phonology, syntax, lexicon) varies with the DIALECTS (or GEOLECTS) of particular regions, the SOCIOLECTS of different social groups or classes, and the sexual differences that make up GENDERLECTS. In fact, each individual has his or her own IDIOLECT, subtly unique in its typical modes of expression. Such variations in LECTS (a neutral term for all varieties) inevitably turn up when we compare two world languages such as Spanish and English, each with some 400 million speakers and still growing.