 A few years after T’oegye’s death, a new Four-Seven debate was ignited, this time between Yi I (pen name: Yulgok) and his friend Sŏng Hon (pen name: Ugye), when the latter sent a letter to the former in 1572. Ugye was an enthusiastic follower of T’oegye’s understanding of the Four-Seven relationship, and thus one can safely assume that Ugye vicariously debated the matter with Yulgok. Following T’oegye, Ugye suggests that the Four Sprouts and Seven Emotions come from Principle and Vital Force respectively. In a famous analogy, Ugye then compares Principle and Vital Force to a rider controlling his horse, just like T’oegye did to explain his alternate issuance theory.