Sociology of religion is the study of the beliefs, practices and organizational forms of religion using the tools and methods of the discipline of sociology. This objective investigation may include the use both of quantitative methods (surveys, polls, demographic and census analysis) and of qualitative approaches (such as participant observation, interviewing, and analysis of archival, historical and documentary materials). Modern sociology as an academic discipline began with the analysis of religion in Émile Durkheim's 1897 study of suicide rates among Catholic and Protestant populations, a foundational work of social research which served to distinguish sociology from other disciplines, such as psychology. The works of Karl Marx (1818-1883) and Max Weber (1864-1920) emphasized the relationship between religion and the economic or social structure of society. Contemporary debates have centered on issues such as secularization, civil religion, and the cohesiveness of religion in the context of globalization and multiculturalism. Contemporary sociology of religion may also encompass the sociology of irreligion (for instance, in the analysis of secular-humanist belief systems). The sociology of religion is distinguished from the philosophy of religion in that it does not set out to assess the validity of religious beliefs. The process of comparing multiple conflicting dogmas may require what Peter L. Berger has described as inherent "methodological atheism". Whereas the sociology of religion broadly differs from theology in assuming indifference to the supernatural, theorists tend to acknowledge socio-cultural reification of religious practice. Classical sociology Classical, seminal sociological theorists of the late 19th and early 20th century such as Émile Durkheim, Max Weber, and Karl Marx were greatly interested in religion and its effects on society. Like those of Plato and Aristotle from ancient Greece, and Enlightenment philosophers from the 17th through 19th centuries, the ideas posited by these sociologists continue to be examined today. Durkheim, Marx, and Weber had very complex and developed theories about the nature and effects of religion. Of these, Durkheim and Weber are often more difficult to understand, especially in light of the lack of context and examples in their primary texts. Religion was considered to be an extremely important social variable in the work of all three. Karl Marx According to Kevin J. Christiano et al., "Marx was the product of the Enlightenment, embracing its call to replace faith by reason and religion by science." But he "did not believe in science for science's sake … he believed that he was also