Slippery slope arguments imply opposition to change.

Abstract

Slippery slope arguments (SSAs) of the form if A, then C describe an initial proposal (A) and a predicted, undesirable consequence of this proposal (C) (e.g., "If cannabis is ever legalized, then eventually cocaine will be legalized, too"). Despite SSAs being a common rhetorical device, there has been surprisingly little empirical research into their subjective evaluation and perception. Here, we present evidence that SSAs are interpreted as a form of consequentialist argument, inviting inferences about the speaker's (or writer's) attitudes. Study1 confirmed the common intuition that a SSA is perceived to be an argument against the initial proposal (A), whereas Study2 showed that the subjective strength of this inference relates to the subjective undesirability of the predicted consequences (C). Because arguments are rarely made out of context, in Studies 3 and 4 we examined how one important contextual factor, the speaker's known beliefs, influences the perceived coherence, strength, and persuasiveness of a SSA. Using an unobtrusive dependent variable (eye movements during reading), in Study3 we showed that readers are sensitive to the internal coherence between a speaker's beliefs and the implied meaning of the argument. Finally, Study4 revealed that this degree of internal coherence influences the perceived strength and persuasiveness of the argument. Together, these data indicate that SSAs are treated as a form of negative consequentialist argument. People infer that the speaker of a SSA opposes the initial proposal; therefore, SSAs are only perceived to be persuasive and conversationally relevant when the speaker's attitudes match this inference.