Description: Buridan's Bridge (also known as Sophism 17) is described by Jean Buridan, one of the most famous and influential philosophers of the Late Middle Ages, in his book Sophismata. Sophism 17 is a self-referenced paradox that involves a proposition pronounced about an event that might or might not happen in the future. The sophism is: Imagine the following scenario: Socrates wants to cross a river and comes to a bridge guarded by Plato, who says: Plato: Socrates, if in the first proposition which you utter, you speak the truth, I will permit you to cross. But surely, if you speak falsely, I shall throw you into the water. Socrates: You will throw me into the water. Buridan's solution In order to solve the paradox Buridan proposes three questions: 1 Is the proposition uttered by Socrates: "You are going to throw me into the water" true, or is it false? 2 Is Plato's promise true or is it false? 3 "What ought Plato to do to fulfill his promise?" In response to the first question Buridan states that it is impossible to determine if Socrates' proposition is true or false. This is because the proposition "You are going to throw me into the water" is a future contingent that could be true or false depending on what Plato is going to do. Dr. Joseph W. Ulatowski says that Buridan apparently used Aristotle's thesis about what "truth" is to come up with this response. Aristotle believed that a proposition is true if and only if it is verified by the state of things as they currently are. Contradicting the principle of bivalence, Buridan implies a system of three-valued logic in which there are three truth values--true, false, and some indeterminate third value. In determining the truth value of Plato's conditional promise, Buridan suggests that Plato's promise was false, and that because Plato gave his promise carelessly he is not obligated to fulfill the promise. In discussing the third question, "What ought Plato to do to fulfill his promise", Buridan states that Plato should not have given a conditional promise in the first place. He also suggests that Plato could have made sure that the condition was formulated in such a way that it would not cause a contradiction; because Plato cannot fulfill his conditional promise without violating it, he is not obligated to fulfill the promise. Ulatowski points out that this is the contrapositive of the principle stated by Immanuel Kant: "ought implies can".