This chapter discusses the critique of scholastic language and philosophy by the Renaissance philosopher and medical writer Francisco Sanches, whose That Nothing Is Known is widely regarded as one of the most systematic expositions of philosophical skepticism produced in the sixteenth century. As this chapter shows, language plays an important role in Sanches’s critique: Aristotelian science does not pay attention to things or facts but is a merely verbal game. Appealing to “what most people say,” Sanches seems to endorse the common language as alternative to the technical terminology of the philosophers. Yet, his skeptical attitude prevents a wholesale endorsement. The chapter then examines Sanches’s critique of two Aristotelian definitions of knowledge. While scholars have attempted to locate Sanches’s discussion of perception and knowledge in the context of late-medieval discussions, the chapter makes clear that Sanches’s position is that of a Renaissance skeptic. He shared the humanists’ utter disdain for what they thought was abstract wordplay, but while their critique of Aristotelian dialectic was part of an educational, didactic project that aimed to transform the traditional trivial arts, bringing dialectic more in line with how people actually speak and argue, Sanches’s goal was to undermine certainty and absolute truth.