The definition of love is the subject of considerable debate, enduring speculation and thoughtful introspection. The difficulty of finding a universal definition for love is typically tackled by classifying it into types, such as passionate love, romantic love, and committed love. These types of love can often be generalized into a level of sexual attraction. In common use, love has two primary meanings, the first being an indication of adoration for another person or thing, and the second being a state of relational status. Love is an act of identifying with a person or thing, capable of even including oneself (cf. narcissism; reverence). Dictionaries tend to define love as deep affection or fondness. In colloquial use, according to polled opinion, the most favored definitions of love involve altruism, selflessness, friendship, union, family, and bonding or connecting with another.
Thomas Jay Oord has defined love in various scholarly publications as acting intentionally, in sympathetic response to others (including God), to promote overall well-being. Oord means for his definition to be sufficient for research in ethics, religion, and science.
The different aspects of love can be roughly illustrated by comparing their corollaries and opposites. As a general expression of positive sentiment (a stronger form of like), love is commonly contrasted with hate (or neutral apathy); as a less sexual and more mutual and "pure" form of romantic attachment, love is commonly contrasted with lust; and as an interpersonal relationship with romantic overtones, love is commonly contrasted with friendship, although other connotations of love may be applied to close friendships as well.
The very existence of love is sometimes subject to debate. Some categorically reject the notion as false or meaningless. Others call it a recently-invented abstraction, sometimes dating the "invention" to courtly Europe during or after the Middle Ages. Others maintain that love really exists, and is not an abstraction, but is undefinable, being essentially spiritual or metaphysical in nature. Some psychologists maintain that love is the action of lending one's "boundary" or "self-esteem" to another. Others attempt to define love by applying the definition to everyday life.
Cultural differences make any universal definition of love difficult to establish. Expressions of love may include the love for a soul or mind, the love of laws and organizations, love for a body, love for nature, love of food, love of money, love for learning, love of power, love of fame, love for the respect of others, etc. Different people place varying degrees of importance on the kinds of love they receive. Love is essentially an abstract concept, easier to experience than to explain. Because of the complex and abstract nature of love, discourse on love is commonly reduced to a thought-terminating cliché, and there are a number of common proverbs regarding love, from Virgil's "Love conquers all" to The Beatles' "All you need is love".