With Valentine's Day this month many of us will be booking restaurants, buying flowers and pretty gifts, or planning something special for that special person in our lives.

I am using this occasion to reflect upon an interesting interpretation of love and relationships that I have been considering for a while.

My Economics professor at Sydney University described the Theory of Decreasing Marginal Utility using what I thought to be a peculiar example. The Theory of Decreasing Marginal Utility as I remember it goes something like this:

"At all instances of consumption where there is a net benefit to be gained, one continues to consume. But the pleasure of consumption gained per unit decreases with each additional unit. When the pleasure gained from one more unit is equal to the displeasure arising from the consumption of that unit, consumption stops."

My lecturer could have demonstrated this in simple terms by using the example of a thirsty man and a glass of water. Imagine it is a hot day and you are out in the sun. You are thirsty, so you pour a glass of water. The first sip is by far the most refreshing as the cool liquid moistens your lips and tongue. The next taste is not quite as refreshing as the first, but is still satisfying, drenching the inners of your dry cheeks. The final gulp does not offer the same relief as either the first or second, but you still feel good. You pour another glass. Depending on your thirst and need for more water you will drink more and more, each sip gradually becoming less and less refreshing. Eventually your thirst runs out, you have no need for more water and you stop drinking.

Rather than use a simple illustration like the one, the professor used the example of love. I assume that he intended to catch the audience's attention with a sexier example. Imagine you are lonely and are looking for love. You start dating somebody you are attracted to. Initially you discover new things about one another, and life is wonderful. Each day or week brings new pleasures and delights. But all the while the pleasure you receive is surely diminishing, whether you like it or not. For he who is in need of love, the initial taste is the most refreshing, each taste afterwards is decreasingly so.

At some stage in the relationship you begin to have passing thoughts about the things you dislike in your partner. They will have some personality trait or quirk that is mildly annoying, most people do, even if the annoyance is a lack of annoying quirks, and will only become increasingly so. Annoyances satisfy no needs and only serve to create a desire for separation. The greater the annoyances, the greater want for distance, and the need for a new love. When the need for distance is equal to the satisfaction provided by your partner, and the risk of finding someone new or better suited is not so great as to be restrictive, you will break up.

This illustration is simple and excludes much of the nuance in human relations. It treats intangible things like love and annoyance in the same way as practicalities, like partnership and separation, as opposites. As an analysis of human action it has shortcomings, as there are more variables at play in relationships aside from simply feeling good or bad, and being together or apart. It neglects to account for the masochists amongst us who need to be tortured in love, or for whom love is founded upon submission, self'denial and sacrifice. It also neglects to account for those who use love to exercise unreasonable power and influence over their partner. As you might well guess, the dominant and submissive tend to work well together.

Aside from these faults, I think the Theory of Decreasing Marginal Utility is a reasonable assessment of how relationships work, certainly when you consider the contemporary urban type. This is not a healthy thing. We have been conditioned by popular culture (Carrie Bradshaw et al) to think that there is always someone out there superior to our current partner. The problem for twenty'somethings is that the perceived harm of breaking up with someone who we are generally happy with is slight. Rather than work through the annoyances and grievances, we choose the easy path and separate. A generation ago the chance of finding someone new and appropriate was far slighter, as it was undesirable to publicly engage anyone with a sexual history, especially for men in pursuit of nubile women; this was left to the confines of clandestine extra'marital affairs. Consider that Princess Diana was expected to be a virginal, innocent and inexperienced bride a little more than 20 years ago. Now consider how few comments have been made about the past of Mary Donaldson, who approached the Danish throne with a history, or much more recently, the vast approval of the majority towards the imminent marriage of Charles and Camilla. Times and expectations have changed.

I do not long for a return to the antiquated values that placed higher regard upon the upkeep of taboos than the well being of citizens. Nor do I advocate partnerships that do not act in the best interests of both parties ' just look what happened to Charles and Diana. But I feel that many of us in our twenties are missing out when we break up with someone for little more reason than because it is too soon to commit to a serious relationship, or that our partner might not be The One, or that there are plenty more fish in the sea. But what if there aren't any good one's? People should be conscious of cultural constructions that suggest there are many opportunities for love and more fulfilling relationships, and should treat these half'truths with caution before they burn bridges and discard what they might live to regret.

Have a happy and uneconomical Valentine's Day!