2.2 Characteristics of Interlanguage
As a unique type of language, interlanguage has the following characteristics:
(1) Interlanguage consists of errors.
The reason why we pay much attention to errors is that they are an obvious feature of learner language. Errors are evidence of the state of a learner’s knowledge of the L2. An error is different from what we call a ‘mistake’. A mistake is akin to slips of the tongue. They are generally one-time-only events. The speaker who makes a mistake is able to recognize it as a mistake and correct it if necessary. An error, however, is systematic. That is, it is likely to occur repeatedly and is not recognized by the learner as an error. The learner in this case has incorporated a particular erroneous form (from the perspective of the TL) into his own system. Errors are not only systematic; many of them are also universal. That is, a kind of error found in one learner’s speech is often attested in the speech of many other learners. What’s more, some errors are common only to learners who share the same mother tongue. Errors can have different sources. Learners may commit errors of omission when they attempt to make the task of learning and using the L2 simpler. For example, they may leave out articles ‘a’ and ‘the’ and leave the –s off plural nouns. They may make overgeneralization errors when they overgeneralize forms that they find easy to learn, as in using ‘eated’ in stead of ‘ate’. Learners also make transfer errors when they attempt to make use of their L1 knowledge. By studying errors, we can see that learners are actively involved in shaping the ‘grammars’ they are learning, and that they are ‘creating’ their own rules.
(2) The learner’s grammar is dynamic.
The system of rules which learners have in their minds changes frequently, or is in a state of flux. This results in a succession of interim grammars. That is, learners change their grammar from one time to another by adding rules, removing rules and reorganizing the whole system. This change is described as discontinuous progression “from stable plateau to stable plateau” (Selinker, 1992: 226). For example, at the beginning, learners may build a very simple grammar in which only one form of the verb is used, such as ‘walk’ used in all cases. But over time, they learn more other forms, such as ‘walking’ and ‘walked’, gradually sorting out the functions these verbs are used to perform.
(3) Interlanguage is a reduced system.
The fact that IL is a reduced system can be proved by the errors learners produce while constructing their grammars. For example, learners who make omission errors are in some way simplifying the learning task by ignoring more complicated grammatical features. In this case, interlanguage is a reduced system, both in form and function. The characteristic of reduced form refers to the less complex grammatical structures that typically occur in an IL compared to the TL. Examples like he borrow a book yesterday belong to reduced form since there is an omission of past tense suffix after the verb borrow. The characteristic of reduced function refers to the smaller range of communicative needs typically served by an IL, especially if the learner is still in contact with members of the L1 speech community. For example, when they want to ask for help, they may use the L1 to perform the function.
(4) Interlanguage is likely to fossilize.
According to Selinker, only about five percent of learners go on to develop the same mental grammar as native speakers. Most learners stop some way short, making no further progress. This kind of phenomenon is called fossilization. The Random House Dictionary of the English Language defines fossilization of a linguistic form, feature, rule, and so forth in the following way: “to become permanently established in the interlaguage of a second language learner in a form that is deviant from the target-language norm and that continues to appear in performance regardless of further exposure to the target language.” (Gass and Selinker, 2008:14) Fossilization refers to a process in second or foreign language learning, in which incorrect linguistic features become a stabilized part of the way a person speaks or writes a language. Aspects of pronunciation, vocabulary usage, and grammar may become fixed or fossilized. Fossilization does not occur in L1 acquisition. It is unique to L2 grammars.

