Critical thinking is embedded in national university graduate outcomes and included in international bodies' statements on higher education. At the same time, there are tensions surrounding critical thinking in higher education, such as its commodification, Eurocentrism, and relationship to rapidly digitalising cultures. Drawing from the philosopher Bernard Stiegler's writings on human originary technicity, this paper argues that critical thinking takes different forms according to technical and cultural milieus. For Stiegler, human originary technicity makes prosthesis the human condition: we are biological and technical, both organic and inorganic matter. Reasoning, reflection, and evaluation are relative to the technologies of memory that form everyday and intellectual culture. Stiegler's analysis articulates how digitalisation threatens and protects reasoning and reflection, enabling the demonstration of how critical thinking takes specific forms in digitalised societies. The paper proposes "prosthetic critical thinking" as a practice that can embrace differing understandings of critical thinking, namely as skills and dispositions associated with reasoning and as the practice of critical pedagogy. The resulting understanding of critical thinking shows it to be a plural, inclusive, and contingent practice relevant to higher education.