Errors made by the first year students of St. Louis I Catholic Senior High School Surabaya in using the English modal auxiliaries

English modal auxiliaries constitutes one of the grammatical items to be mastered by the first year students of senior high school. However, when the writer carried out her teaching practice, she found that many students still had difficulties in using the English modal auxiliaries. This situation led the writer to do a study on analyzing the students' errors in using the English modal auxiliaries. In conducting this study, the writer gave a test to the first year students of SMAK St. Louis I Surabaya. Class I1 was as the try-out group while class I2 , I3 and I4 were as the sample group. From the students' test papers, the writer got the data needed. Then, the errors made by the students were noted down, classified in two ways. One according to the types and the other according to the modal auxiliaries discussed in this study. After being classified, the errors were put in a rank order. According to the types, the errors that the students made were classified into ignorance of rule restrictions and false concepts hypothesised. While according to the modal auxiliaries, the errors were classified into errors in modal auxiliary 'Will', errors in modal auxiliary 'Would', errors in modal auxiliary 'Shall', errors in modal auxiliary 'Should', errors in modal auxiliary 'Can', errors in modal auxiliary 'Could', errors in modal auxiliary 'May•, errors in modal auxiliary 'Might', and errors in modal auxiliary 'Must'. The findings of the study showed that the first year students of SMAK St. Louis I Surabaya did made errors in using the English modal auxiliaries, and the errors are ranked from the highest to the lowest one: false concepts hypothesised (=80.12%) and ignorance of rule restrictions (=19.88%) according to the types; errors in modal auxiliary 'Shall' (=18.8%), errors in modal auxiliary 'Would' <= 13.8%), errors in modal auxiliary 'May' (=13%), errors in modal auxiliary 'Must' (=12%), errors in modal auxiliary 'Will' (=9.9%), errors in modal auxiliary 'Might' (=9.6%), errors in modal auxiliary 'Could' (=9.6%), errors in modal auxiliary 'Should' (=6.8%), and errors in modal auxiliary ‘Can’ ( =6. 5%). At last, the writer hopes that the findings of this study could give better information about how the students lear the English modal auxiliaries, so that teachers can improve their techniques in teaching the English modal auxiliaries