Choice behavior can be influenced by many different types of incidental contextual effects, including those pertaining topresentation format, emotion, social belief, and cognitive capacity. Many of these contextual effects form the basis ofnudges, used by academics and practitioners to shape choice. In this paper, we use data from a very large-scale choiceexperiment to uncover a space of contextual effects. We construct this space by analyzing fifteen contextual effects usingthe parameters of the drift diffusion model (DDM). DDM is a quantitative theory of decision making whose parametersoffer a theoretically compelling characterization of the cognitive underpinnings of choice behavior. By representing a largenumber of contextual effects in terms of how they influence the parameters of the DDM, our space is able to preciselymeasure, quantify, and compare the contextual effects, and interpret these effects in terms of their behavioral, mechanistic,and statistical implications.