Love encompasses a range of strong and positive emotional and mental states, from the most sublime virtue or good habit, the deepest interpersonal affection, 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 for food. Most commonly, love refers to a feeling of a strong attraction and emotional attachment.Love is considered to be both 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 potentially leading 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 that keeps human beings together against menaces and to facilitate the continuation of the species.Ancient Greek philosophers identified six forms of love: essentially, familial love (in Greek, Storge), friendly love or platonic love (Philia), romantic love (Eros), self-love (Philautia), guest love (Xenia), and divine love (Agape). Modern authors have distinguished further varieties of love: unrequited love, empty love, companionate love, consummate love, infatuated love, self-love, and courtly love. Numerous cultures have also distinguished Ren, Yuanfen, Mamihlapinatapai, Cafuné, Kama, Bhakti, Mettā, Ishq, Chesed, Amore, Charity, Saudade (and other variants or symbioses of these states), as culturally unique words, definitions, or expressions of love in regards to a specified "moments" currently lacking in the English language.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.