A few weeks ago I was giving a morning's teaching on the topic of human rights and in the course of the morning I sought to get across three fundamental points. The first point was that the breakthrough achieved by the issuing of the Universal Declaration of Human Rights in 1948 was the formal recognition that everyone, whoever they are, and wherever they live, have certain basic rights simply because they are human beings.

The second point was that the concept of rights is inextricably bound up with the concept of obligations. As the Christian theologian Nicholas Wolterstorff argues in his book Justice rights and wrongs, we cannot talk about the one without talking about the other. The language of rights, he argues, gives voice to the truth that human beings have an obligation to treat other human beings in certain morally good ways, and that those other human beings are wronged if they are not treated in this way. In his words, 'One is guilty if one has failed to do what one was obligated to do; one is wronged if one has not been treated as one had a right to be treated.'

What this means is that the criticism that is sometimes made about the notion of human rights, that it is all about rights and says nothing about duties, is misplaced. Obligation and duty mean the same thing, the way one ought to behave, and as we have just seen, rights and obligations necessarily go together. I cannot coherently insist that my rights should be observed, without also accepting that I have an obligation to observe the rights of others.

The third point was that human rights have to be grounded in an understanding of natural rights. Human rights, strictly so called, are those rights which have been recognised in national and international law. This fact begs the question which rights should be so recognised and the answer to this question can only be based on the idea that there is a moral order within which human beings have a right to be treated in certain ways. When Christian theologians have talked about 'natural rights' this is what they have meant.

Such rights are 'natural' because within the moral order that God established at creation those creatures possessed of a human nature should be treated in certain ways and are wronged if this is not the case. For example, the idea of a natural 'right to life' means that the life of a human being should be respected and not brought to an end without good cause, and that a human being is wronged when this is not the case (as when someone is murdered, or executed for a crime they did not commit).

I was stimulated to think about these three points again this week because of a report from the Christian Institute about criticism of the Republic of Ireland by the human rights campaign group Amnesty International for allowing medical staff to refuse to carry out abortions.

The report stated: 'Medics in the Republic of Ireland should not be allowed to refuse to carry out abortions on religious or ethical grounds, Amnesty International has said. The organisation's Executive Director in Ireland, Stephen Bowen, claimed pro-life medics were "failing" pregnant women by causing them to travel overseas for an abortion. Amnesty, which advocates for the decriminalisation of abortion, says human rights protections only "start at birth" and labels laws limiting access to abortion as "human rights violations."'

What really interested me about this report was the last sentence with its insistence that human rights only start at birth. I wondered if Amnesty International had really said this and, if so, how they justified saying it, and so I looked up what Amnesty International themselves actually said.

When I looked at their documents on the matter online, I found that their document Amnesty International's policy on abortion key messages does indeed declare that: 'Human rights start at birth. The updated abortion policy recognises that human rights protections start at birth. In other words, international human rights law and standards do not recognize so-called foetal rights or human rights applications to foetuses, embryos, zygotes or gametes. While Amnesty does not take a position on when human life begins, as this is a moral and ethical question for individuals to decide for themselves, its policy is aligned with international human rights law and standards that confirm that human rights protections start at birth, not before.'

This claim is difficult to defend on two grounds. The first is that while international human rights standards do indeed state positively that human beings have rights from birth (thus Article I of the Universal Declaration of Human Rights states: 'All human beings are born free and equal in dignity and rights'), none that I am aware of deny that the unborn child has rights before that point.

Secondly, unless human rights laws and standards are to be totally arbitrary in what they declare, any claim that an unborn child does not have rights would have to be based on a natural law understanding of when human life begins.

Amnesty International's professed agnosticism on this point ('Amnesty does not take a position on when human life begins') does not make any moral sense. This is because if God has so created the world that human life begins at conception (as biology tells us that it does) then the life of an unborn child from that point onwards is a human life and can thus be argued to have the protection that is due to all human life (as the International Covenant on Civil and Political Rights puts it 'Every human being has the inherent right to life').

Furthermore, even if one held that human life might begin at conception then what is known as the 'precautionary principle' in ethics would mean that one would have an obligation to take this possibility into account and treat life in the womb as human life and therefore entitled to have its life protected. The point here is that if one concludes that life in the womb is human life after one has killed it, then it is too late to go back and rectify the error. Barring a miracle, we cannot resurrect the dead.

The only secure moral ground for allowing abortion would be the certainty that human life begins at birth and Amnesty International offers no grounds for believing that such certainty exists.

If we go on to look for a positive reason why Amnesty International supports abortion, the reason that it puts forward is the principle of 'reproductive autonomy.' As its website on 'Abortion rights' puts it: 'International human rights law clearly spells out that decisions about your body are yours alone – this is what is known as bodily autonomy. The right to make autonomous decisions about one's reproductive life is known as reproductive autonomy.'

The condensed argument that is being offered here is that human rights law says that human beings have the right to decide what to do with their body and a subset of this general right is the freedom to make decisions 'about one's reproductive life' (hence 'reproductive autonomy').

What this argument ignores is the fact that human rights law, and the principle of human rights in general, does not say that I have absolute freedom to do what I like with my body. As I noted at the beginning of this article, rights and obligations go together. Thus, if I as a human being have a right to education, then this comes with a corresponding obligation to recognise that all other human beings have a right to education (and to act accordingly). In similar fashion, if I as a human being have the right to have my right to life protected, then this comes with the obligation to respect the right to life of all other human beings.

Applying this argument to the claim that human beings should be recognised as having 'reproductive autonomy', we can acknowledge that there is no absolute moral obligation to have children. In Christian terms the command to 'be fruitful and multiply' in Genesis 1:28 applies to human beings in general, not to every human being in particular. It follows from this that human beings should have the freedom to decide whether to have children. Forcing a woman to become pregnant (or a man to father a child) would thus be morally wrong. In this sense the idea of a right to 'reproductive autonomy' makes sense.

However, if a child has been conceived then the picture changes. This is because if human life starts at conception, then what exists in a woman's womb is not part of her body but another human being, and neither her right to bodily autonomy nor anyone else's desire to bring the pregnancy to an end (such as a father wanting to 'get rid of that baby') can override that human being's right to life and the moral obligation to respect this. The basic ethical principle here is the one previously noted, namely that someone's life could only be brought to an end if there is a very good cause for doing so, and the mere fact that another person (or persons) don't want someone to live does not count as a very good cause - otherwise it would be open season for murder.

At this point someone might bring up the issue of what should happen if a pregnancy threatens the life of a mother. Is it legitimate to terminate the pregnancy to save the life of the mother in this circumstance? Here the ethical principle known as 'double effect' comes into play. This says that it would not be legitimate to intend to kill an unborn child, but it could be legitimate to save the mother in a way that had the tragic but undesired effect of killing the child. For example, suppose a pregnant woman has a cancerous uterus which if left in place will kill her (and thereby her unborn child). In this situation it is impossible to save both the mother and the child, but the mother's life can be saved if the uterus is removed. In this case although removing the uterus will kill the unborn child this could be seen as the least-worst moral option.

We need to acknowledge that such cases can occur (though thankfully they are rare), but we cannot then make them the basis for an unrestricted right to abortion.