Opera latina XXXI = op. 13-16

Lullus' Quattuor libri principiorum were developed from the Ars compendiosa inueniendi ueritatem. Lullus wrote them probably near by the period 1274-1283. In them we find the main rules of Lullian art in an early stage, as a muster of his universal knowledge system. These books are here set together to show the unity of method for theology, philosophy and justice. The traditional matters about medicine are explained with the other logical constraints proved as a standard. The chapters on generation and corruption, fever, urine and pulse show the extent theory of humours and the optimal levels of the four natural elements, preventive treatments, and the means to recover from illness. The book Principia medicinae is the only one that has parallel textual Catalan tradition.