The current trend is to choose not to have children. All over the West birth rates are falling. And I am asking why.

I have two different worries about this fall in population. My first anxiety is that sterilisation on the NHS uses up the service's money. Moreover, some people change their minds and later want the operation reversed.

Second, when you are teaching people about ethics one of the things you say is: "what if everybody did it?" In moral philosophy that question goes back to Immanuel Kant's principle of universability. There are some things you cannot universalise. If everybody committed suicide, for instance, we would all be wiped out. So when people make the decision to remain childless voluntarily, the decision does not just affect the couples themselves.

The trouble with the baby boom generation is that our parents were war generation parents. They wanted us to have all the things they did not have and as a result we are totally self-centred. My parents and grandparents would be quite happy to sacrifice themselves for the sake of others. We, however, believe in rights, in autonomy, we believe that the world owes us everything. This generation of students is the same, it thinks the world owes it a living. And the reality is, it does not. So I am uneasy about the sociological, moral and political pressures that are driving people to make decisions about voluntary childlessness.

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I think we do have a responsibility to procreate. That does not mean to say every single human being has to have children - otherwise we would be saying: "Go out and procreate whenever you can find someone." That kind of sex is wrong.

But one of the questions individuals need to ask when considering whether to have children is: "Do I not have a responsibility to society?" I can sympathise with some of their concerns, such as what kind of a world am I bringing a child into or what effect might my child have on the world. (Hitler had parents.) But one of the things I want couples to do is ask:

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"What if everyone chose to remain childless?"

David Cook Chaplain and fellow of Green College, Oxford