<![CDATA[The language used in instructional materials plays a crucial role in maintaining clarity of delivery and the effectiveness of the learning process. This study aims to describe (1) sentence errors without a subject, (2) sentence errors without a predicate, and (3) disruptions between main clauses and subordinate clauses in the Teaching Module and Essential Material for Grade X Mathematics at MAN Purworejo. This research is a qualitative study. The subjects of the study are the Teaching Module and Essential Material for Grade X Mathematics at MAN Purworejo. The population of this research includes all data contained in the Teaching Module and Essential Material, totaling 206 pages, from which 186 data points were obtained. The data collection technique used in this research is the literature technique. The research instrument employed is the human instrument. The data analysis consists of the following steps, data collection, data reduction, data presentation, and conclusion drawing. The results of the study show that the researcher found three types of sentence errors in the Teaching Module and Essential Material for Grade X Mathematics at MAN Purworejo: the absence of a subject, the absence of a predicate, and disruptions between main clauses and subordinate clauses. In the first type of error, 48 sentences were identified. Several sentences begin with verbs, causing the subject to be absent and rendering the sentences incomplete. The second type of error appears in 5 sentences. These sentences either lack a predicate or contain a predicate that does not correspond to the subject, resulting in a failure to fulfill the S–P (Subject–Predicate) sentence pattern and making the sentences ineffective. As for the third type of error, 133 sentences were found. These involve the improper use of subordinating conjunctions such as "to, if, then, and that," causing subordinate clauses to violate or stand without the appropriate main clause. Overall, a total of 186 sentence errors were identified. These various errors indicate a lack of carefulness in constructing sentence structures, which affects reading comprehension, learning effectiveness, and the clarity of information received. Improvements in accordance with Indonesian syntactic rules are necessary so that the sentences in the module are presented more clearly, systematically, and easily understood by students.]]>
