 Aquinas, as with Aristotle, exhibits no serious concerns with skepticism or with skeptical arguments. He occasionally makes references to sensory illusions, e.g., but he sees them as no epistemological threat. Baertschi (1986) and Pasnau (1997) treat of this issue briefly. Indeed, most of the secondary literature on Aquinas focuses on the question of why he has no such interest in skepticism. Varying accounts are given, and among them is Aquinas’s Aristotelian belief that the cognitive process is fundamentally a reliable one. For the most part, Aquinas and most later medievals aim to explain the processes by which knowledge is acquired, rather than aiming to justify knowledge.