This paper will present Robert Brandom’s Rational Expressivism and the possible applications of his proposed pragmatic meta-vocabularies in human-computer interaction (HCI). In the German idealist tradition, rationality is not merely the ability to make decisions in individual practice but is the foundation of intersubjective communication and norm-setting in practical communities. In a systematic reworking of the Kantian and Hegelian concepts of rationality, Brandom offered a set of ways to account for how human beings rationally engage in practice with each other. The central idea of his approach is that rationality is enacted in shared practice as a set of practical procedures, which can be expressed as reasonable steps with the help of linguistic structures. For example, pragmatic meta-vocabularies such as modal words can express inferences about possible counterfactual cases. This line of thought is an adaptation of German Idealism using language analysis and a functionalist approach to the anthropological apprehension of human beings as rational beings. After introducing his theory, this paper will show why this idea can be extended to human technological practices in general and HCI in particular, and how pragmatic meta-vocabularies can be integrated into the design of frameworks for HCI.