Personalism in the broadest sense is the philosophical view that understands person to be the highest reality and the fundamental principle of explanation. Personalists are usually philosophers and theologians standing within the theistic tradition who use the concept of person to distinguish theistic from monistic views which tend to threaten the independence of persons. Personalism has its antecedents in personal idealism discussed in the first part of this book, and some of the personalists discussed in this chapter might well have been included among them. Since the first world war, however, personalism has become more independent of the idealist tradition, and in many cases the emphasis upon freedom and action has brought it in close proximity to existential philosophy. In a more narrow sense, personalism may designate the philosophical movement in the United States that is often called the school of Boston Personalism.