The Preliminary and Main exams in UPSC differ significantly in purpose and structure. The Preliminary exam serves as a screening tool, consisting of objective-type questions that test basic understanding of subjects and general knowledge. Its primary function is to filter candidates for the next stage. In contrast, the Main exam is more comprehensive and consists of descriptive-type questions, assessing candidates' in-depth knowledge and analytical skills across various subjects. The Main exam also includes a personal interview, allowing for assessment of candidates’ personality and suitability for public service roles, thus making both exams crucial yet distinct in evaluation.