Defending the view that Karl Jaspers' concept of irrationality (Widervernunft) is better able to account for pathological patterns of individual and collective thinking, Karl Jaspers' Theory of Irrationality: From Delusions to Worldviews argues that irrationality is incorrigibility, a blockage of reason as the will to communication. Highlighting the importance of freedom and creativity at the heart of reason (Vernunft), Daniel Adsett analyzes examples of delusional thought through a Jaspersian lens. He shows that irrationality arises when we hold to certain attitudes with an incorrigible conviction and refuse to genuinely consider the possibility that we might need to revise or change our beliefs. In presenting these arguments, Adsett offers a novel contribution to contemporary debates about the character of reason while rehabilitating an often neglected aspect of Jaspers' thought.