The first, descriptive task naturally requires a clarification of one's terms—above all, the word "religion". Historians of religion have long underscored the problematic character of this term, noting that its usage over the centuries has changed in significant ways, generally in the direction of reification. The early psychologists of religion were fully aware of these difficulties, typically acknowledging that the definitions they were choosing to use were to some degree arbitrary. With the rise of positivistic trends in psychology over the course of the 20th century, especially the demand that all phenomena be operationalized by quantitative procedures, psychologists of religion developed a multitude of scales, most of them developed for use with Protestant Christians. Factor analysis was also brought into play by both psychologists and sociologists of religion, to establish a fixed core of dimensions and a corresponding set of scales. The justification and adequacy of these efforts, especially in the light of constructivist and other postmodern viewpoints, remains a matter of debate.