Pascal Boyer argues that while there is a wide array of supernatural concepts found around the world, in general, supernatural beings tend to behave much like people. The construction of gods and spirits like persons is one of the best known traits of religion. He cites examples from Greek mythology, which is, in his opinion, more like a modern soap opera than other religious systems. Bertrand du Castel and Timothy Jurgensen demonstrate through formalization that Boyer's explanatory model matches physics' epistemology in positing not directly observable entities as intermediaries. Anthropologist Stewart Guthrie contends that people project human features onto non-human aspects of the world because it makes those aspects more familiar. Sigmund Freud also suggested that god concepts are projections of one's father.