Falling in love is the development of strong feelings of attachment and love, usually towards another person.
The term is metaphorical, emphasising that the process, like the physical act of falling, is sudden, uncontrollable and leaves the lover in a vulnerable state, similar to "fall ill" or "fall into a trap".
It may also reflect the importance of the lower brain centers in the process, which can lead the rational, accounting brain to conclude (in John Cleese's words) that "this falling in love routine is very bizarre....It borders on the occult".
"Factors known to contribute strongly to falling in love include proximity, similarity, reciprocity, and physical attractiveness", while at the same time, the process involves a re-activation of old childhood patterns of attachment. Deep-set psychological parallels between two people may also underpin their pairing-bonding, which can thus border on mere narcissistic identification".
Two chemical reactions associated with falling in love are increases in oxytocin and vasopressin; and Elisabeth Young-Bruehl has suggested that "when we fall in love we are falling into a stream of naturally occurring amphetamines running through the emotional centres of our very own brains". With regard to sociobiology, it is stressed that mate selection cannot be left to the head alone and must require complex neurochemical support.
Critics of such Neo-Darwinism point out that over-simplistic physical arguments obscure the way sexual passion often leads not to secure attachment but to attachments thwarted, as well as the sheer frightening difficulties of all falling in love.
Stendhal charted the timing of falling in love in terms of what he called crystallization--a first period of crystallization (of some six weeks) which often involves obsessive brooding and the idealisation of the other via a coating of desire; a period of doubt; and then a final crystallization of love.
Empirical studies suggest that men fall in love earlier than women and women are quicker to fall out of love than men.
While some consider falling in love to be the nearest approach to a spiritual experience possible for the non-religious, others say its loss of ego boundaries is merely a temporary phenomenon which has little to do with, or may even block, spiritual development.