Love, like happiness, is easier to experience than it is to define. One of the reasons it is so hard to define is because it is so complex, but the complex nature of love need not deter us in our quest to understand it.

For most people, love is an emotion, a feeling of affinity that they have for another person. So to understand love we must first understand more about emotion. I would argue that there is rarely, if ever, such a thing as pure emotion. Feelings are tied to a number of bodily and external factors. Take away any one of those factors and you remove the emotion. Let's look at another feeling to see how this works. For the purpose of this exercise I'll describe another common emotion, anxiety.

• Firstly there is a stimulus, a fierce dog for example.
• Secondly there is perception: you see the dog.
• Thirdly there is thought: you think to yourself, "That's a mean looking dog. He might bite me and I'll have to have stitches in my leg. It'll hurt. Oh my God, get me out of here".
• Fourthly there is a physical reaction; pulse increases, muscle tension increases, bladder and bowels request evacuation, etc.
• Fifthly you act, you do something. In the case of the dog, you make a hasty retreat.

Love follows a similar pattern. Let's look at the beginning of a love affair and watch as it progresses and you'll see these five factors in action.

• Firstly there is the stimulus. There is another person, perhaps a stranger on the other side of a crowded room.
• Secondly you see the stranger, possibly on an enchanted evening.
• Thirdly you think to yourself, "Mmm, s/he looks cute".
• Fourthly your body begins to react, heart rate, muscles, perhaps even genitals signal their interest in proceedings.
• Fifthly, you approach the stranger and initiate a conversation.

At this stage what you feel is probably not love, but could be called curiosity, attraction, lust, etc. The name you give to the emotion probably depends on the thoughts that you're having. For love to exist, the relationship requires time and the further interaction of the five factors. Let's follow this budding affair as it develops into a full-blown love affair.

• Firstly the stimulus. Your new friend acts kindly towards you.
• Secondly you see and feel his/her kindness.
• Thirdly you think "God s/he's gorgeous. I love him/her". Etc etc.
• Fourthly you have goosebumps down your spine.
• Fifthly you return your lover's kindness with another kindness.

And so it goes on. You react cognitively, bodily and behaviourally whenever your lover stimulates you, and s/he reacts similarly towards you.

So to define love we need to take in all these aspects into consideration and say that love is a pleasant or favourable cognitive-physical-behavioural response towards another person. Love is maintained and intensified whenever your lover acts in a way that provokes the pleasant or favourable cognitive-physical-behavioural response in you. Similarly, the love that your partner feels for you is intensified whenever you provoke a similar response in him/her. Love is made more intense and enduring by repeating the cycle as frequently as possible.

Rational love versus irrational love.
I don't believe that there is such a thing as rational love or irrational love. Rationality is a quality that applies to thinking and so only applies to the third aspect of love, not to the entire emotion. Some people speak of behaving irrationally, however, I regard this as a misuse of the word. A better term would be 'self-defeatingly'. Let's look at how a person in love could think irrationally and behave self-defeatingly.

Irrational thoughts are ones that cannot be supported by evidence or that don't make sense. Let's examine two of the most common irrational thoughts held by people in love.

• I need him/her.
• S/he is wonderful.

Both these thoughts sound good, but neither makes sense or can be supported by any evidence. In the case of the first one, the speaker is confusing a strong desire for a need. There are very few things that we need in life. We need air, water, food and shelter. But apart from that we don't really need anything. Everything else is a bonus that adds to the quality of life. While I wouldn't advocate living on these things alone, it can be useful to remind ourselves regularly that we have very few needs, but lots of genuine and legitimate wants, including the love of another person.

The second thought is an example of people-rating. We all have a mixture of traits, some of which we like, some we are neutral about and some we don't like. It is possible to rate these traits, to give them a mark out of, say 100, but it isn't possible to do that with an entire person because we wouldn't know which traits to include, how to balance the good ones against the bad ones and so on.

In the case of love there is probably little real harm done by this kind of irrational thinking. However, taken to an extreme, it can lead to self-defeating behaviour and that is where the harm is done.

Self-defeating behaviour can include such things as obsessive-compulsive behaviour where all other interests suffer because you are so busy thinking about and devoting yourself to your 'wonderful' lover whom you 'need'. It can lead to sycophantic behaviour and the ignoring of your own wishes in order to satisfy your lover's demands. It can lead to depression and perhaps suicide when your love is unrequited.

This is just a partial list of the ways that people behave self-defeatingly when they think irrationally about their partner.

How to love and be loved.
When you find yourself in the company of someone with whom you would like to enjoy a relationship, employ the following guidelines.

• When s/he acts kindly towards you, respond with similar kindness. Repeat regularly.
• Learn to distinguish between your needs and your wants.
• Rate your lover's behaviour but not your lover as a person.
• Avoid getting into the habit of subordinating your own interests.