How might these reasons be rationalized in terms of their connection to elements of the rhetorical situation? 

Question 3. Penrose and Katz, in their chapter “Reading and Writing Research Reports”, describe a variety of high-level, argumentative, and linguistic patterns which are generic to scientific research articles. Importantly, however, they ground these observations in the rhetorical situation by describing the venues in which these articles appear and the way these articles are constructed, read, and referred to. This grounding presents the opportunity to recognize multiple (often simultaneous) rationales for the structures observed.
Consider specifically citation in journal articles. What are two (or more) co-existing reasons the authors of the chapter list for research article authors to cite the work of others? How might these reasons be rationalized in terms of their connection to elements of the rhetorical situation?  And how might those rationalizations be used to supplement Hyland’s empirical/linguistic discussion of citation patterns?