Proposition is the "bone marrow" of the paper, the central argument that runs through the paper, and a basic problem or viewpoint that you try to discuss or demonstrate in the paper. If a paper has no proposition, it is not a real paper. At most, it is like a textbook with the name of a paper, just like a uniform building with doors, windows and eaves. Thesis usually refers to discussion, debate or demonstration, so its basic requirement is to demonstrate around the proposition. An introductory article may play a role in expanding the academic perspective, but it should not be the main research mode in academic circles.