Love. Love encompasses a range of strong and positive emotional and mental states, from the most sublime virtue or good habit, the deepest interpersonal affection and to the simplest pleasure. An example of this range of meanings is that the love of a mother differs from the love of a spouse, which differs from the love of food. Most commonly, love refers to a feeling of strong attraction and emotional attachment. Love is considered to be a positive and negative: with its virtue representing human kindness, compassion, and affection, as the unselfish loyal and benevolent concern for the good of another; and its vice representing human moral flaw, akin to vanity, selfishness, amour-propre, and egotism, as it potentially leads people into a type of mania, obsessiveness or codependency. It may also describe compassionate and affectionate actions towards other humans, one's self or animals. In its various forms, love acts as a major facilitator of interpersonal relationships and, owing to its central psychological importance, is one of the most common themes in the creative arts. Love has been postulated to be a function to keep human beings together against menaces and to facilitate the continuation of the species. Ancient Greek philosophers identified five forms of love: essentially, familial love, friendly love or platonic love, romantic love, guest love and divine love. Modern authors have distinguished further varieties of love: unrequited love, empty love, companionate love, consummate love, infatuated love, self-love, and courtly love. Scientific research on emotion has increased significantly over the past two decades. The color wheel theory of love defines three primary, three secondary and nine tertiary love styles, describing them in terms of the traditional color wheel. The triangular theory of love suggests intimacy, passion and commitment are core components of love. Love has additional religious or spiritual meaning. This diversity of uses and meanings combined with the complexity of the feelings involved makes love unusually difficult to consistently define, compared to other emotional states.The word love can have a variety of related but distinct meanings in different contexts. Many other languages use multiple words to express some of the different concepts that in English are denoted as love; one example is the plurality of Greek words for love which includes agape and eros. Cultural differences in conceptualizing love thus doubly impede the establishment of a universal definition. Although the nature or essence of love is a subject of frequent debate, different aspects of the word can be clarified by determining what isn't love. Love as a general expression of positive sentiment is commonly contrasted with hate. As a less-sexual and more-emotionally intimate form of romantic attachment, love is commonly contrasted with lust. As an interpersonal relationship with romantic overtones, love is sometimes contrasted with friendship, although the word love is often applied to close friendships or platonic love. Abstractly discussed, love usually refers to an experience one person feels for another. Love often involves caring for, or identifying with, a person or thing, including oneself. In addition to cross-cultural differences in understanding love, ideas about love have also changed greatly over time. Some historians date modern conceptions of romantic love to courtly Europe during or after the Middle Ages, although the prior existence of romantic attachments is attested by ancient love poetry. The complex and abstract nature of love often reduces discourse of love to a thought-terminating cliche.