Karen races excitedly to the front door. Will there be anything for her in the post? Yes! There on the mat is a large pink envelope. Who can it be from? With trembling fingers she tears it open to find a beautiful card. And there is a message - but a very strange one: "Be my storge Valentine!" What on earth does it mean?

According to the psychologist John Alan Lee, ¹ there are six basic types of love that define people. One style is likely to dominate, though it is possible to feel a mixture of them.

First-sight delight "Eros" is a romantic, intense and immediate love in which physical attraction is very important. People who feel it love being in love - so if the initial excitement fades, they tend to turn to someone new in order to experience the feeling again.

Company harmony "Storge" is a more stable form of love, involving a lot of commitment and trust. Those who feel it value companionship, so they choose partners with similar interests; physical attractiveness is less important. It often develops from friendship.

Shameless game "Ludus" is the Latin word for "game", which is how some people view love. They tend to be low on commitment, more led by physical attraction, and liable to use manipulation and deceit. They often start a new relationship before ending an existing one.

Practical tactics "Pragma" is a practical type of love. It emphasises compatibilityWhen two people get on together without problems or conflict. and whether the other person will meet your needs. You look for someone who will get on with your friends and family, and has the ability to make life smoother for you.  

Crazy fantasy "Mania" involves obsession, possessiveness and feeling extreme highs and lows. It demands constant reassurance in a relationship, and often leads to feelings of jealousy.  

Unsparing caring "Agape" is unselfish and unconditional love. It involves caring for the other person's needs and loving them just as they are. If both partners feel agape, they are likely to be extremely happy together.  

The Ancient Greeks believed in three further types of love. "Philia" was love for family and friends. "Philautia" was love of oneself. "Xenia" was respect for guests and strangers.

Psychologists distinguish between "passionate" and "companionate" love. "Passionate" involves an intense longing for someone; "companionate" involves feeling comfortable with them and committed to them. In many relationships the first gradually gives way to the second.

NeuroscientistsA scientist who studies the brain and the nervous system.  have found that passionate love causes increased brain activity, with the release of chemicals such as dopamineA hormone and neurotransmitter that plays several important roles in the brain and body, providing us with positive sensations, rewarding us for evolutionarily good behaviours like eating food. which produce feelings of euphoria and happiness. Thinking about people you are fond of does not have the same effect.

Evolutionary scientists believe that love developed to keep couples together until their children were old enough to fend for themselves. Since childhood lasts much longer for humans than for other species, it was more important for us than for animals.

Yes: Happiness and sadness are the result of chemicals released by our brains. Fear developed to help keep us safe from danger. Love evolved so that children would be properly looked after.

No: Love is a wonderful, indefinable thing that cannot be reduced to chemical formulas or evolutionary theories. Poets and songwriters have a much better understanding of it than scientists do.

Or... Evolutionary science explains why most humans want to find a mate and reproduce. But it is impossible to say why some couples are happy together or predict whether a marriage will last.