The paper explores the rhetorical potential of modal adverbs and it brings an interactional dimension to the study of legal genres. In agreement with Traugott (2010), it follows the view that "very little language use is purely monologic" and that speakers and writers frequently position themselves towards alternative viewpoints, contesting or refuting counterarguments and expressing doubt. To this end, based on data from adversarial proceedings, US Supreme Court oral arguments and written opinions as well as Opinions of the Advocates General at the European Court of Justice, the study examines the functional spectrum of modal adverbs distinguished by Simon-Vandenbergen and Aijmer (2007). As revealed by the analysis, the interpersonal meanings conveyed by the adverbs found in the corpus include politeness and solidarity, on the one hand, and power and authority, on the other.