The syllabus for the UPSC prelims differs from the mains examination in terms of scope and depth. The prelims encompass multiple-choice questions that assess general awareness, current affairs, and basic subject knowledge, while the mains consist of written examinations that require elaborate, analytical answers across various subjects. The mains place greater emphasis on critical thinking, essay writing, and comprehension, necessitating a deeper understanding of topics compared to the preliminary phase, which primarily tests factual knowledge.