 The linchpin of Epictetus’s entire philosophy is his account of what it is to be a human being; that is, to be a rational mortal creature. “Rational” as a descriptive term means that human beings have the capacity to “use impressions” in a reflective manner. Animals, like humans, use their impressions of the world in that their behavior is guided by what they perceive their circumstances to be. But human beings also examine the content of their impressions to determine whether they are true or false; we have the faculty of “assent” (1.6.12–22).