Both men had already been cooperating in the development of a uniquely Christian philosophy and their labours began to see considerable fruit over the next ten years. The mid-1930s saw a series of significant publications culminating in Dooyeweerd’s magnum opus "De Wijsbegeerte der Wetsidee" (The Philosophy of the Cosmonomic Idea) in three volumes. At this time Vollenhoven organised the "Association for Calvinistic Philosophy" which he served as president until his retirement in 1963, by then an international organisation with over 500 members. Dooyeweerd became the first editor of the Association's academic journal "Philosophia Reformata".