The advent of the digital computer has rendered logic diagrams and manipulatives into historical footnotes. Nevertheless, they are significant in the historical development of logic as an area of mathematics. In this book Gardner describes the various ways syllogisms and propositions have been represented in diagrams, but he also spends a great deal of time explaining the personalities. Ramon Lull was quite a character. Early in life he was a hedonist, but due to a religious vision, was converted into somewhat of a religious fanatic. While some groups considered him divinely inspired and he has been beatified, the Dominicans considered him a madman and his prolific writings contain a great deal that could be considered heretical. He even wrote a book containing dialogues in which he and a priest argue as to which one has had the most preposterous life. On three occasions, he made pilgrimages to Moslem cities in Africa in order to engage in religious debates with Islamic leaders and point out the errors inherent in Islam. The first two times he managed to escape with his life, but the last time, at the age of 83, he was stoned to death by a mob. In many ways, it is thought of as his way of committing suicide. His logic diagrams were a set of circular manipulatives that could be rotated to create different combinations of symbols. Various symbols represented God, the soul, sins, virtues and other elements of religious belief. While they are of interest, after reading of his rather eventful life, they seem anticlimactic.