The perennial problem of not cleaning after oneself in self-service hawker centres has stumped most civic-minded people.

So charging for trays is one example of a desperate hope to change the diehard habit of not bothering to clear one's table after eating (Charging for trays can help change attitudes, by Miss Tan Lin Neo; Feb 1).

Singaporeans are familiar with the use of fines as disincentives to punish undesirable social habits.

We have earned our reputation as a "fine" city since the introduction of such measures a long time ago.

But we have failed most miserably with such measures.

Yet, there are still advocates who insist on using money as a disincentive to effect behavioural change.

I would suggest we reverse the equation: Use money as a reward or incentive for good social habits.

Instead of charging for the non-return of trays, give a voucher for a free meal or item, such as a dessert of one's choice, for tray return. I suspect this would have more success.

Thomas Lee Hock Seng (Dr)