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Conquering Our Imagination:
Thought Experiments and Enthymemes in Scientific Argument
University of Pittsburgh
The dividing line between rhetoric and science has traditionally been drawn at the split between persuasion and logic. On the one side, rhetoric seeks to influence human beliefs and behavior through use of stylistic language that resonates with the experiences of an audience; on the other, science endeavors to describe empirical phenomena through the use of logical propositions that can be understood wholly on their own terms. However, recent scholarship has blurred this border. For instance, in his research on Charles Darwin's rhetorical accomplishments, John Angus Campbell has sought to break down "the neopositivist Berlin Wall separating the context of discovery from the context of justification" that represents this traditional division (1990, 23). Claiming that scientific discovery and rhetorical invention are each "an aspect of a flexible logic of inquiry and presentation" (23), Campbell argues that "the social and theological ring of Darwin's language is not merely decorative or ameliorative, but is constitutive of the fabric of his thought" (5). In other words, Campbell insists there is something intrinsically valuable about Darwin's frequent use of colloquial language beyond its immediate rhetorical appeal—it also contributes something fundamental to scientific knowledge itself.
This "something," according to Campbell, is the necessary connection between argument and audience that inspires scientific theorizing and culminates in the establishment of new scientific paradigms. Within the context of discovery, the potential rhetorical audience works as a motivating force in the invention of persuasive arguments. That is why, when Darwin's notebooks are closely examined, it can "be said that virtually every note Darwin penned . . . was written with an eye to a public, often in response to a nameable individual" (1990, 23). Then, within the context of justification, the actual rhetorical audience works to literally fill in the necessary gaps in any rhetorical argument. That is why Darwin, in order to [End Page 21] tap into this resource, "embedded his central insight in a preexisting common world of thought and feeling" (4). Finally, it is for both of these reasons that one cannot fully reconstruct Darwin's "core concept of his argument as a logical proposition shorn of its colloquial language and associations" (4). For Campbell, "the danger in setting aside Darwin's language is that we effectively remove half of the problem he addressed and disregard the intelligence required to address it—how to present a radical idea to a particular scientific and popular audience in a way that retains the persuasive force of the very tradition it destroys" (5).
Campbell's claim that rhetoric is constitutive and cannot be boiled away through logical or reductive analysis asserts the centrality of both stylistic language and audience within the process of scientific argumentation. However, although it is clear that rhetoric has a role to play during revolutionary moments in the history of science, it is not as clear that contemporary audiences cannot go directly to the logical reconstructions of past theories without any significant loss of cognitive value. Thus, we must ask whether a scientific argument, when removed from its immediate persuasive context, can nonetheless be "shorn of its colloquial language and associations" in order to reveal its logical core. What, in other words, is the relationship between the logic of scientific argumentation, the rhetorical appeal of language, and the participation of an audience?
This essay suggests that a tentative answer can be found by approaching the question through the concept of the "thoughtexperiment." Thought experiments are distinguished from traditional experiments by their explicitly hypothetical quality. Instead of seeking immediately verifiable empirical results, they are designed to invite an audience to visualize a set of initial conditions and then imagine what might happen in response to those conditions. Galileo, for instance, authored one of the most famous thought experiments when he speculated what would happen if two objects of different weights were tied together and dropped. Einstein tried to envision what we might see from a clear box...