At the age of 87, several years after he had stopped writing, Isaiah Berlin responded to an invitation from a Chinese professor to summarize his ideas for publication in China. He produced an extraordinary essay that defended moral pluralism and warned against its enemy, moral monism (or moral absolutism), which he defined as the thesis that "to all true questions there must be one true answer and one only, all the other answers being false." He then wrote:Most revolutionaries believe, covertly or overtly, that in order to create the ideal world eggs must be broken, otherwise one cannot obtain the omelette. Eggs are certainly broken-never more violently or ubiquitously than in our times-but the omelette is far to seek, it recedes into an infinite distance. That is one of the corollaries of unbridled monism, as I call it-some call it fanaticism, but monism is at the root of every extremism. (Berlin, 1998) In this essay we build upon Berlin's idea 1 and argue that the elevation or "sacralization" of a moral principle or symbol is a major cause of evil. This idea has been developed quite ably by others in recent years (see Baumeister, 1997, this volume, on "idealistic evil"; Glover, 1999, on tribalism;and Skitka & Mullen, 2002, and Skitka, this volume, on the "dark side" of moral convictions). We hope to add to these analyses of morality and evil by offering a map of moral space which may be helpful in explaining why so many different principles and objects can become sacred, along with an account of how sacredness permits and motivates different patterns of evil behavior.We begin by defining our key terms -sacredness and morality. We then introduce Moral Foundations Theory as a way of broadening and mapping the moral domain, and thereby identifying diverse kinds of sacred objects. In the third section we show how this moral foundations approach can also broaden our view of evil, and we offer a definition of evil based on group-level perceptions of threats to sacralized objects. In the fourth section we take a qualitative approach to sacredness, showing how two diametrically opposed moralities can both lead to idealistic violence. In the fifth section we introduce the Moral Foundations Sacredness Scale, a simple instrument that can be used to measure the degree to which people sacralize each of the five foundations of morality. We conclude by considering unanswered questions about which foundational values are most likely to lead to idealistic violence.