Defuse is a new method for navigating and participating in online discussions. Previous designs for online discussion were successful under the assumption that participation would be limited to tens or at most hundreds of participants. Emergent social conventions have been able to smooth over media as they scale, but ultimately they are limited by the design of a medium itself. Defuse seeks to continue scaling online discussions by adding social, structural, and historical context throughout the interface, and by widening the expressivity of a message to match the user's intention. It does so using a combination of natural language processing, machine learning, visualization, data portraiture, social network analysis, and medium design.