a biochemical dimension driven through reactions in the body stimulated by sexual attraction (PEA, phenylethylamine), and a social dimension driven by "talk" that follows from regular physical closeness or sexual union. Love is an important factor in emotional intimacy. It is qualitatively and quantitatively different from liking, and the difference is not merely in the presence or absence of sexual attraction. There are three types of love in a relationship: passionate love, companionate love, and sacrificial love. Sacrificial love reflects the subsumption of the individual self-will within a union. Companionate love involves diminished potent feelings of attachment, an authentic and enduring bond, a sense of mutual commitment, the profound feeling of mutual caring, feeling proud of a mate's accomplishments, and the satisfaction that comes from sharing goals and perspective. In contrast, passionate love is marked by infatuation, intense preoccupation with the partner, throes of ecstasy, and feelings of exhilaration that come from being reunited with the partner. Cognitive or intellectual intimacy takes place when two people exchange thoughts, share ideas and enjoy similarities and differences between their opinions. Spiritual intimacy involves bonding over spirituality. Research Empirical research The use of empirical investigations in 1898 was a major revolution in social analysis. A study conducted by Monroe examined the traits and habits of children in selecting a friend. Some of the attributes included in the study were kindness, cheerfulness and honesty. Monroe asked 2336 children aged 7 to 16 to identify "what kind of chum do you like best?" The results of the study indicated that children preferred a friend that was their own age, of the same sex, of the same physical size, a friend with light features (hair and eyes), friends that did not engage in conflict, someone that was kind to animals and humans, and finally friends that were honest. Two characteristics that children reported as least important included wealth and religion. The study by Monroe was the first to mark the significant shift in the study of intimate relationships from analysis that was primarily philosophical to those with empirical validity. This study is said to have finally marked the beginning of relationship science. In the years following Monroe's study, very few similar studies were done. There were limited studies done on children's friendships, courtship and marriages, and families in the 1930s but few relationship studies were conducted before or during World War II. Intimate relationships did not