This paper examined the types of the conditional clause and analyzed the frequency of the conditional clause currently used in the texts of high school textbooks and reviewed a teaching plan how to teach the conditional clause in school. The conditional clause can be divided into 2 types of the real condition and the unreal condition in the traditional grammar by Leech (1971). The real condition is a state in which truth and falsity of a statement are not decided in the main clause and the subordinate clause and is truth-neutral. The unreal condition means an assumption opposite to a fact, impossible state or infeasible state or contents which haven't been achieved yet or was not achieved in the past.
Currently, education in class English unconditionally depends on textbooks for teacher's instructional objects, methods and contents. English textbooks play a mediating role in connecting English educational theories and policies with actual education fields and are important teaching materials directly influencing learning activities of learners in English teaching courses.
Therefore, this study analyzed the English textbooks by selecting I and II for 2nd and 3rd graders in high schools who completed the 2009 Revised Educational Curriculum. The distribution of the conditional clause shown in the textbooks and frequency ranking about the semantic types were compared and analyzed through the textbooks. From this analysis, the authenticity aspect of the textbooks could be examined and a more effective learning of the conditional clause and a teaching plan could be suggested.
Effective teaching plans for the learning of the conditional clause can be summarized to 3 types and first, it should avoid the teaching method focused on formulated types. Second, it is necessary to clearly classify and explain the semantic differences of the real conditional clause and the unreal conditional clause. Both the two types use if-clause but cause big semantic differences. Even though the interpretations could be the same, it should emphasize different usage according to situations in teaching. Third, after acquisition of contexts through reading and writing activities, the guidance to confirm whether they are fully understood semantically through the speaking activity is required. The interpretation of the conditional clause can be made differently according to situations. Students should be taught and encouraged to well understand the situation contexts of the front and back sentences and to themselves understand the semantic parts about the real condition and the unreal condition after teaching and to speak in the speaking activity by dividing the parts.
Because in general, the conditional clause has a low frequency in the textbooks, learners and teachers may not put importance on the grammar domain of the conditional clause. ELF learners are not exposed a lot to the sentences about the conditional clause so that teachers should put their effort to emphasize them when teaching. As mentioned on instruction measures, it is an essential grammar domain to practice and learn because EFL learners make frequent errors when selecting tenses.