It is suitable the reality that making errors is a part of learning a language. The interference of native to target language or the different underlying assumptions between the native and target one can be the sources of errors.
Richards (1974:174-181) states there are some causes of errors. They are as follows:
1. Over-generalization
The learner has the tendency to simplify the formations or the rulers of the target language. It seems that the learner tends to use the simple rules to generalize the uses. In the past tense, for example, we should add-ed to the regular verb. Thus, the learner may produce * You finded the book yesterday or * Did you walked to school this morning?
The learner also often mixes the rules learned previously with the present rules taught. The learner over learners of structure which many pattern interferes with each other. Fox example, She runs with she is running: She swims with She can swim. The, the learner produces * She can swims.
2. Ignorance of Rules Restrictions
It is still closely related to over-generalization. In this case the learner violates the restriction of existing structure. This the application of rules to contract where they do not apply. The examples of this type are * The girl who I saw her, * Mother let her to go.
Some of this type of errors is as a result of false analogy, especially in using preposition. The learner who uses a particular preposition with one type of verb will use the same preposition with similar verbs. For example, She said to may * She asked to me; They talked about it leads to * They discussed about it; Ask her to do it produces * make her to do it.
3. Incomplete Application of Rules.
It happens due to the deviation of structure that neglects the development of rules to produce the acceptable sentences. For example, in teaching foreign language, teacher often uses questions as a teaching device to get the learner’s responses. The learner’s incomplete knowledge of the target language make him neglect the rules of the target language make him or giving response to the teacher’s questions. Some examples are as follows:
Teacher’s Questions Student’s Responses
Do you read much? * Yes, I read much
Does he like the newspaper? * Yes, he likes.
Ask him how much it costs. * How much it costs?
What does he tell her? * He tell her to study hard.
4. False Concepts Hypothesized.
It happens due to misconception of the difference in the target language. The poor teaching techniques, sometimes, creates this faulty comprehension. In the teaching of present tense, for example, The teacher usually start with the teaching of to be: am, is, are, then teaching the verbs. In the teaching of past tense the teacher follows the same sequence. If the teacher presents the items poorly, the learner may have a false conclusion: am, is, are are the signs of present activities and was, were, are the signs of past activities. So, the learner may produce sentences such as * He is comes late, * They are football every Sunday, * We were studied English yesterday.