According to Jervis, many political psychology thinkers developed prescriptive and descriptive theories. By this, he means that these frameworks attempt to provide a strictly empirical account and infer normative statements of how policymakers ought to behave. However, Jervis notes that these theories fail to predict behavior accurately when actors do not act in accordance with the hypotheses. This goes to show that even adequately trained scholars cannot be completely objective.
Jervis claims that even the most abstract theories are not free of the personal preferences of theorists. At the end of the day, it is not exactly reasonable to believe that any scholar with a solid, informed opinion will be changed or even slightly influenced by opposite views. In a sense, every theory reflects the political inclinations of theorists to a certain extent. As an example, Jervis mentions Kenneth Waltz, from whose theory of international politics it can be inferred that the US should not have to wage war against Vietnam. As Jervis notes, it is unclear whether Waltz’s political presuppositions informed the theory or vice versa.
Nevertheless, Jervis acknowledges that inventing a theory lacking the prescriptive aspect would be very difficult. As he says, “this would be difficult because by telling a decision-maker how others behave, an explanatory theory would lead to prescription” (Jervis, 2017, p. 128). He takes this point further by proposing that even if a theorist provided a purely explanatory account of political behavior, interpreters of the text would nonetheless project their moral values onto the theory. In short, Jervis’s point comes down to the impossibility of eliminating personal bias, as either the scholar or the audience will derive a prescription via the projection of personal inclinations and values.
Jervis, R. (2017). How statesmen think: The psychology of international politics. Princeton University Press.