LIKE MANY teenagers in the Auckland neighbourhood where I grew up, I drove my own car to school. Our parents had not given us these cars. We bought them ourselves with money saved from working after school and during holidays. Our parents thought that giving us cars would be bad for us. In New Zealand, back then, parents were careful not to spoil their children. They preferred the long-term kindness of cultivating a work ethic in their children to the short-term kindness of lavish gifts.

This tension, between “tender compassion” and “tough compassion”, lies at the heart of social policy as well as parenting. The tender impulse favours policies that give immediate help to the suffering: generous unemployment benefits, free healthcare, pension supplements for old people without savings and so on. Yet anything that lessens the pain of a predicament also lessens the incentive to avoid it, and so increase the amount of it. Tough compassion opposes tender policies.

Consider the compassion shown to poor single mothers and their children. The State provides them with free housing, education and healthcare, subsidised transport and enough cash for basic clothing and household expenses. And to ensure that every child has “the best start in life”, the Sure Start programme now provides all manner of extra assistance.

Very tender. But disastrous in terms of incentives. Short of making them positively rich, I cannot think of a better scheme for increasing the number of single mothers. In 1972, 6 per cent of British children were raised by single mothers. Today, 22 per cent are. The same story can be told around the Western world.

I know tender types who dismiss this talk of incentives. “Look at how tough things are for single mothers,” they declare. “Would you go through all that for a council house and the paltry cash benefits?” No, I wouldn’t. Nor would most reading this article. But that is irrelevant. Incentives work at the margins. Increasing unemployment benefit will have no effect on an investment banker’s propensity to work, but it might change the inclinations of someone who would otherwise be earning the minimum wage. Equally, it is not socially concerned Guardian readers whose breeding behaviour will be affected by state subsidies, but those whose opportunities are much more limited in the first place.

The argument also displays a restricted view of how, and on whom, the incentives for single motherhood work. Women do not consciously choose to become single mothers on the basis of a financial calculation. Rather, it is the consequence of living in a culture whose mores are adapted to the economics of tender policies.

Why should a man not abandon his partner and child? Guilt and shame would once have prevented most men from even considering it. In the days before the State supported single mothers, a man who abandoned his wife and children did them great harm. He could only hate himself and be hated by society.

But what harm does he do them now? When the State will house, feed and educate a man’s wife and children, he may abandon them and lose neither sleep nor friends. By changing the economics of single motherhood, the State has changed the morality of it. It has created a sub-culture of reproductive irresponsibility.

We can have happier single mothers or we can have fewer single mothers, but not both. The tender and the tough sides of compassion really are at odds with one another. And not just with regard to single mothers. Give more money to pensioners with no savings and we will have more pensioners with no savings. Give the obese more free medical treatment and there will be more obesity. The laws of incentives are no less real, nor their consequences more avoidable, than the laws of physics.

The ideal social policies lie somewhere on the spectrum between tough and tender. Striking the right balance between the tough and the tender is a difficult job. But it is not difficult to know the direction in which British policy has gone wrong. Since the Second World War it has been overrun by tenderness. This Government has continued the trend, increasing taxation and directing ever more support towards the worst off.

New Labour takes incentives seriously in business, where efficient resource allocation requires that companies be allowed to fail and their owners lose money. But in social policy it clings to the Utopian fantasy that the possibility of suffering can be eliminated without creating perverse incentives. New Labour abides by the Marxist principle: “From each according to his ability, to each according to his need.” Delightful to the tender ear but, to the tough ear, a recipe for a population with few abilities and many needs.

David Cameron promises to be a compassionate Conservative. Let’s hope he remembers that a compassionate Conservative is also a conservative. A conservative rejects Utopianism. He does not see the human condition through the veil of socialist fantasy. He recognises the real trade-off between tender and tough compassion. And he tends to be tough — though no less compassionate for that.

Jamie Whyte is a philosopher and author of Bad Thoughts: A Guide to Clear Thinking

Times Recommends

• It’s the beginning of the affair
• Afghanistan: still a price worth paying
• Heroes of the downtrodden