I and Thou, Martin Buber's classic philosophical work, is among the 20th century's foundational documents of religious ethics. "The close association of the relation to God with the relation to one's fellow-men ... is my most essential concern," Buber explains in the Afterword. Before discussing that relationship, in the book's final chapter, Buber explains at length the range and ramifications of the ways people treat one another, and the ways they bear themselves in the natural world. "One should beware altogether of understanding the conversation with God ... as something that occurs merely apart from or above the everyday," Buber explains. "God's address to man penetrates the events in all our lives and all the events in the world around us, everything biographical and everything historical, and turns it into instruction, into demands for you and me." Throughout I and Thou, Buber argues for an ethic that does not use other people (or books, or trees, or God), and does not consider them objects of one's own personal experience. Instead, Buber writes, we must learn to consider everything around us as "You" speaking to "me," and requiring a response. Buber's dense arguments can be rough going at times, but Walter Kaufmann's definitive 1970 translation contains hundreds of helpful footnotes providing Buber's own explanations of the book's most difficult passages.