Most studies about students' conceptions and conceptual change are based exclusively on the analysis language, which is treated as a tool to make private contents of the mind public to researchers. Following recent studies that focused on (a) language and discursive practice and (b) the pragmatics of communication that draws on talk, gestures, and semiotic resources in the setting, we propose a redefinition of the nature of conception. Conceptions are understood as the dialectical relation of simultaneously available speech, gestures, and contextual structures that cannot be reduced to verbal rendering because gestures and contextual structures constitute different modalities in the communication. Drawing on data collected during a physics unit about gas taught in French tenth grade classrooms, we show why an appropriate account of conceptions requires: (a) gestures simultaneously produced with talk; and (b) identification of the relevant structures in the setting used by the participants as meaning-making (semiotic) resources. We propose to: (a) reconceptualize the notion of conception as consisting of a dialectical unit of all relevant semiotic (meaning-making) resources publicly made available by a speaker (talk, gesture, context); and (b) consider conceptual change through the temporal evolution of the dialectical unit defined in this manner. © 2006 Wiley Periodicals, Inc. J Res Sci Teach 43: 1086–1109, 2006