Shakespeare’s Julius Caesar is remarkable for its rational mode as manifested in the use of language, style, action as well as its characterization. In this essay, I argue that the play is also striking with its numerous(ir)rational ambiguities. The same Latin word, ratio, is at the root of two words that are often used to explain human behaviors: reason and rationality. The fi rst related ambiguity is organized around the confl ict between reason and passion. The other is related to rational choice, which is opposed to the diverse forms of irrationality. This paper argues that Julius Caesar challenges the idea that a rational actor is one who acts only for sufficient reasons, and the play also subverts the conventional understanding of reason and rationality. Shakespeare’s Julius Caesar is remarkable for its rational mode as manifested in the use of language, style, action as well as its characterization. In this essay, I argue that the play is also striking with its numerous (ir) rational ambiguities. The same Latin word, ratio, is at the root of two words that are often used to explain human behaviors: reason and rationality. The fi rst related ambiguity is organized around the confl ict between reason and passion. which other is related to rational choice, which is opposed to the diverse forms of irrationality. This paper argues that Julius Caesar challenges the idea that a rational actor is one who acts only for sufficient reasons, and the play also subverts the conventional understanding of reason and rationality.