 One of the most distinctive features of Vives’ study of the human soul is the fundamental role that psychological inquiry came to play in his reform program. His use of psychological principles in his writings often surpasses that of previous authors in both scope and detail. He applies these principles, for instance, not only to individual conduct and education, but also to professional practice, social reform, and practical affairs in general. According to Vives, psychology is relevant to all disciplines. “The study of man’s soul”, he writes in De tradendis disciplinis, “exercises a most helpful influence on all kinds of knowledge, because our knowledge is determined by the intelligence and comprehension of our minds, not by the things themselves” (VI, 375).