The relation of different theoretical approaches to one another is a disquieting question in International Relations (IR). Building on recent scholarship addressing the logic of questions and the analytical tools the scholarship provides for investigating the contributions of different explanations this piece argues that any and all explanations are an answer to a contrastive why-question. First, the article presents the objections to eclecticism. It then reviews the application of the logic of questions to IR and develops a “contrast theory” clarifying this logic: Seeking an explanation means delimiting a contrast space within a specific interrogatory context. The article lastly shows how these concepts help in thinking about post-foundational science of IR, that is, a science with no universal epistemological foundation to knowledge. I argue that the pragmatic, problem-driven and complexity-sensitive research agendas are a stronger foundation than currently predominant conceptualizations. An example, drawn from Iran's attempts to acquire nuclear weapons, helps illustrate the value-added by a logic of questions approach.