In this chapter, we focus on speculative reasoning that makes the past a provisional site for new inquiry and productive possibilities. It opens the past to reveal hidden realities that shape current-day realities or offer new possibilities for the present or future. Such speculations are offered here as modes of inquiry in design research. We discuss speculative practices in feminism, Afrofuturism, more-than-human epistemologies, disability studies, and decolonization as they relate to design and technologies. Like the previous chapters, we examine the workings of speculative reasoning through the framework of leaps of imagination, diverse epistemologies, ethical reflexivity, and experiential alternatives. We also argue that similar considerations of the past and speculative reasoning have been important to design research and design more broadly through discussions of design games in participatory design, ethnomethodology, critical literature reviews, and analytical accounts of pasts related to HCI.