There are many different theories that attempt to explain what love is, and what function it serves. It would be very difficult to explain love to a hypothetical person who had not himself or herself experienced love or being loved. In fact, to such a person love would appear to be quite strange if not outright irrational behavior. Among the prevailing types of theories that attempt to account for the existence of love there are: psychological theories, the vast majority of which consider love to be very healthy behavior; there are evolutionary theories that hold that love is part of the process of natural selection; there are spiritual theories that may, for instance consider love to be a gift from God; there are also theories that consider love to be an unexplainable mystery, very much like a mystical experience.
Setting aside Empedocles's view of Eros as the force binding the world together, the roots of the classical philosophy of love go back to Plato's Symposium. From its riches, we may perhaps single out three main threads that would continue to reverberate through the centuries that followed.
The idea of two loves, one heavenly, one earthly. As Uncle Toby was informed, over two millennia later, "of these loves, according to Ficinus's comment on Valesius, the one is rational - the other is natural - the first...excites to the desire of philosophy and truth - the second, excites to desire, simply".
Aristophanes's conception of mankind as the product of the splitting in two of an original whole: Freud would later draw on this myth - "everything about these primaeval men was double: they had four hands and four feet, two faces" - to support his theory of the repetition compulsion.
Plato's sublimation theory of love - "mounting upwards...from one to two, and from two to all fair forms, and from fair forms to fair actions, and from fair actions to fair notions, until from fair notions he arrives at the notion of absolute beauty".
Aristotle by contrast placed more emphasis on philia (friendship, affection) than on eros (love); and the dialectic of friendship and love would continue to be played out into and through the Renaissance, with Cicero for the Latins pointing out that "it is love (amor) from which the word 'friendship' (amicitia) is derived" Meanwhile Lucretius, building on the work of Epicurus, had both praised the role of Venus as "the guiding power of the universe", and criticised those who become "love-sick...life's best years squandered in sloth and debauchery".
Among his love-sick targets, Catullus, along with others like Héloïse, would find himself summoned in the 12C to a Love's Assize. From the ranks of such figures, and perhaps also under Islamic influences, would emerge the concept of courtly love; and from that Petrarchism would form the rhetorical/philosophical foundations of romantic love for the early modern world.
Alongside the passion for merging that marked Romantic love, a more sceptical French tradition can be traced from Stendhal onwards. Stendhal's theory of crystallization implied an imaginative readiness for love, which only needed a single trigger for the object to be imbued with every phantasised perfection.Proust went further, singling out absence, inaccessibility or jealousy as the necessary precipitants of love.Lacan would almost parody the tradition with his saying that "love is giving something you haven't got to someone who doesn't exist". A post-Lacanian like Luce Irigaray would then struggle to find room for love in a world that will "reduce the other to the same...emphasizing eroticism to the detriment of love, under the cover of sexual liberation".
Given what Max Weber called the intimate relationship between religion and sexuality, the role of the lingam and yoni in India, or of yin and yang in China, as a structuring form of cosmic polarity based on the male and female principles, is perhaps more comprehensible. By way of maithuna or sacred intercourse,Tantra developed a whole tradition of sacred sexuality, which led in its merger with Buddhism to a view of sexual love as a path to enlightenment: as Saraha put it, "That blissful delight that consists between lotus and vajra...removes all defilements".
More soberly, the Hindu tradition of friendship as the basis for love in marriage can be traced back to the early times of the Vedas.
Confucius is sometimes seen as articulating a philosophy (as opposed to religion) of love.