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,^{[citation needed]} 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".

Scientific views

Main article: Love (scientific views)

Throughout history, philosophy and religion have done the most speculation on the phenomenon of love. In the last century, the science of psychology has written a great deal on the subject. In recent years, the sciences of evolutionary psychology, evolutionary biology, anthropology, neuroscience, and biology have added to the understanding of the nature and function of love.

Biology of love

Further information: Interpersonal chemistry

Biological models of sex tend to view love as a mammalian drive,^{[citation needed]} much like hunger or thirst. Helen Fisher, a leading expert in the topic of love, divides the experience of love into three partly-overlapping stages: lust, attraction, and attachment. Lust exposes people to others, romantic attraction encourages people to focus their energy on mating, and attachment involves tolerating the spouse long enough to rear a child into infancy.

Lust is the initial passionate sexual desire that promotes mating, and involves the increased release of chemicals such as testosterone and estrogen. These effects rarely last more than a few weeks or months. Attraction is the more individualized and romantic desire for a specific candidate for mating, which develops out of lust as commitment to an individual mate forms. Recent studies in neuroscience have indicated that as people fall in love, the brain consistently releases a certain set of chemicals, including dopamine, norepinephrine, and serotonin, which act similar to amphetamines, stimulating the brain's pleasure center and leading to side-effects such as an increased heart rate, loss of appetite and sleep, and an intense feeling of excitement. Research has indicated that this stage generally lasts from one and a half to three years.^[7]

Since the lust and attraction stages are both considered temporary, a third stage is needed to account for long-term relationships. Attachment is the bonding which promotes relationships that last for many years, and even decades. Attachment is generally based on commitments such as marriage and children, or on mutual friendship based on things like shared interests. It has been linked to higher levels of the chemicals oxytocin and vasopressin than short-term relationships have.^[7]

In 2005, Italian scientists at Pavia University found that a protein molecule known as the nerve growth factor (NGF) has high levels when people first fall in love, but these levels return to as they were after one year. Specifically, four neurotrophin levels, i.e. NGF, BDNF, NT-3, and NT-4, of 58 subjects who had recently fallen in love were compared with levels in a control group who were either single or already engaged in a long-term relationship. The results showed that NGF levels were significantly higher in the subjects in love than as compared to either of the control groups.^[8]

Psychology of love

Further information: Human bonding

A couple kissing. Kissing can be viewed as a physical action brought forth by love.

Psychology depicts love as a cognitive and social phenomenon. Psychologist Robert Sternberg formulated a triangular theory of love and argued that love has three different components: Intimacy, Commitment, and Passion. Intimacy is a form by which two people can share secrets and various details of their personal lives. Intimacy is usually shown in friendships and romantic love affairs. Commitment, on the other hand, is the expectation that the relationship is going to last forever. The last and most common form of love is sexual attraction and passion. Passionate love is shown in infatuation as well as romantic love. This led researchers such as Yela^{[citation needed]} to further refine the model by separating Passion into two independents components: Erotic Passion and Romantic Passion.

Following developments in electrical theories, such as Coulomb's law, which showed that positive and negative charges attract, analogs in human life were developed, such as "opposites attract". Over the last century, research on the nature of human mating, such as in evolutionary psychology, agree that pairs unite or attract to each other owing to a combination of opposites attract, e.g. people with dissimilar immune systems tend to attract, and likes attract, such as similarities of personality, character, views, etc.^[9] In recent years, various human bonding theories have been developed described in terms of attachments, ties, bonds, and or affinities.

Some Western authorities disaggregate into two main components, the altruistic and the narcissistic. This view is represented in the works of Scott Peck, whose works in the field of applied psychology explored the definitions of love and evil. Peck maintains that love is a combination of the"'concern for the spiritual growth of another", and simple narcissism.^[10] In combination, love is an activity, not simply a feeling.

Philosophical views

People, throughout history, have often considered phenomena such as "love at first sight" or "instant friendships" to be the result of an uncontrollable force of attraction or affinity.^[11] One of the first to theorize in this direction was the Greek philosopher Empedocles, who in the 4th century BC argued for the existence of two forces, love (philia) and strife (neikos), which were used to account for the causes of motion in the universe. These two forces were said to intermingle with the classical elements, i.e., earth, water, air, and fire, in such a manner that love served as the binding power linking the various parts of existence harmoniously together.

Later, Plato interpreted Empedocles' two agents as attraction and repulsion, stating that their operation is conceived in an alternate sequence.^[12] From these arguments, Plato originated the concept of "likes attract", e.g., earth is attracted to earth, water to water, and fire to fire. In modern terms this is often phrased in terms of "birds of a feather flock together".

Bertrand Russell describes love as a condition of "absolute value", as opposed to relative value. Thomas Jay Oord defines love as acting intentionally, in sympathetic response to others (including God), to promote overall well-being. Oord means for his definition to be adequate for religion, philosophy, and the sciences. Robert Anson Heinlein, one of the most prolific science fiction writers of the 20th century, defined love in his novel Stranger in a Strange Land as the point of emotional connection which leads to the happiness of another being essential to one's own well being. This definition ignores the ideas of religion and science and instead focuses on the meaning of love as it relates to the individual.

Also, an ancient proverb states that love is a high form of tolerance. This view is one that many philosophers and scholars have researched, and is widely accepted.