in a ritual, they are able to signal that they are the authority of the ritual, thus reinforcing the social contract in place. He explains the hierarchical demission of liturgical orders, in which he breaks down four elements of ritual. "Ultimate sacred postulates" form the top of the hierarchy, which are the most fundamental elements of religion. They tend to acquire sanctity over time, since they are often vague and unable to be disproven. Next, he describes cosmological axioms which describe the basic nature of the universe. Following these axioms come the rules that govern interactions and conduct. The fourth point he makes is about the understandings of the external world, where changes occur as a response to the conditions. These points he provides show these adaptive changes help to preserve the system as a whole. Rappaport developed as a well-respected contributor to the field and its subsequent discourse by the coinage and adaptation of new anthropological concepts. He is known for his distinction between "cognized models" and "operational models," in which the former looked at reality and adaptations in how a people's culture understands nature. The cognized model, according to Rappaport, is the "model of the environment conceived by the people who act in it," (Wolf, 1999, 19). The operational model on the other hand, is one "which the anthropologist constructs through observation and measurement of empirical entities, events and material relationships. He takes this model to represent for analytic purposes, the physical world of the group he is studying.... as far as actors are concerned, it has no function," Rappaport explains (Wolf, 1999, 19). In his article "Risk and the Human Environment", he examines the studies of risk to the "human environment," which have been legally mandated by the government for environmental and resource planning. He emphasizes variables such as economic, social and physical properties, which all must be taken into account. He provides an example of a hypothetical oil spill which severely damaged marine life. White fishermen may consider the spill an economic loss; however, for a Native American tribe, the damage would be far more devastating to their subsistence lifestyle. This article in particular stresses the need to further explore the natures of the human environment, and not make a generalization when considering possible risks (Rappaport, 1996, 65). Rappaport served as Chair of the Department of Anthropology, University of Michigan. He also was a past president