There are many things we might consider when thinking through Aquinas’s Natural Law Theory. There are some obvious problems we could raise, such as the problem about whether or not God exists. If God does not exist then the Eternal Law does not exist and therefore the whole theory comes tumbling down. However, as good philosophers we ought always to operate with a principle of charity and grant our opponent is rational and give the strongest possible interpretation of their argument. So, let’s assume for the sake of argument that God exists. How plausible is Aquinas’s theory? There are a number of things that we can pick up on.
Aquinas’s theory works on the idea that if something is “natural”, that is, if it fulfils its function, then it is morally acceptable, but there are a number of unanswered questions relating to natural.
We might ask, why does “natural” matter? We can think of things that are not “natural” but which are perfectly acceptable, and things which are natural which are not. For example, wearing clothes, taking medication and body piercing certainly are not natural, but we would not want to say such things are morally wrong.
On the other hand we might consider that violence is a natural response to an unfaithful partner, but also think that such violence is morally unacceptable. So it is not true that we can discover what is morally acceptable or not simply by discovering what is natural and what is not.
Put this worry aside. Recall, Aquinas thinks that reproduction is natural and hence reproduction is morally acceptable. This means that sex that does not lead to reproduction is morally unacceptable. Notice that Aquinas is not saying that if sex does not lead to pregnancy it is wrong. After all, sometimes the timing is not right. His claim is rather that if there is no potential for sex to lead to pregnancy then it is wrong. However, even with this qualification this would mean a whole host of things such as homosexuality and contraception are morally wrong. We might take this as a reason to rethink Aquinas’s moral framework (we discuss these apparent problems in more detail in Chapter 10).
There is, though, a more fundamental worry at the heart of this approach (and Aristotle’s) to ethics. Namely, they think that everything has a goal (telos). Now, with some things this might be plausible. Things such as the eye or an acorn have a clear function — to grow, to see — but what about humans? This seems a bit less obvious! Do humans (rather than our individual parts) really have a telos? There are certainly some philosophers — such as the existentialists, for example Simone de Beauvoir (1908–1986) — who think that there is no such thing as human nature and no such thing as a human function or goal. But if we are unconvinced that humans have a goal, then this whole approach to ethics seems flawed.
Next we might raise questions about DDE. Go back to our example about abortion. For Aquinas it is morally acceptable to remove the uterus even if we know that in doing so the foetus will die. What is not morally acceptable is to intend to kill the foetus by removing the uterus. On first reading this seems to makes sense; we have an intuitive feel for what DDE is getting at. However, when we consider it in more detail it is far from clear.
Imagine two doctors who (apparently) do exactly the same thing, they both remove the uterus and the foetus dies. The one intends to take out the uterus — in full knowledge that the foetus will die — the other intends to kill the foetus. For the DDE to work in the way that Aquinas understands it, this difference in intention makes the moral difference between the two doctors. However, is there really a moral difference? To put pressure on the answer that there is, ask yourself what you think it means to intend to do something. If the first doctor says “I did not intend to kill the foetus” can we make sense of this? After all, if you asked her “did you know that in taking out the uterus the foetus would die?” she would say “yes, of course”. But if she did this and the foetus died, did not she intend (in some sense) to kill the foetus? So this issue raises some complex question about the nature of the mind, and how we might understand intentions.
Finally, we might wonder how easy it is to work out what actually to do using the Natural Law. We would hope our moral theory gives us direction in living our lives. That, we might think, is precisely the role of a moral theory. But how might it work in this case?
For Aquinas, if we rationally reflect then we arrive at the right way of proceeding. If this is in line with the Natural Law and the Divine Law then it is morally acceptable. If it is out of line, then it is not. The assumption is that the more we think, the more rational we become, the more convergence there will be. We’ll all start to have similar views on what is right and wrong. But is this too optimistic? Very often, even after extensive reflection and cool deliberation with friends and colleagues, it is not obvious to us what we as rational agents should do. We all know people we take to be rational, but we disagree with them on moral issues. And even in obviously rational areas such as mathematics, the best mathematicians are not able to agree. We might then be sceptical that as rational agents we will come to be in line with the Natural and Divine Laws.