Aquinas believed that Humans obey the Synderesis rule, “we seek the good and avoid evil.” However, this appears to only be true for apparent goods, like contraception, as many people do things that seem good but are against God’s will. But is everyone inclined towards the good? Many people do wrong despite knowing it, for instance vandals. Another point criticising the Synderesis rule is that Darwin’s theory of ‘survival of the fittest’ implies that Humans are self-interested.
One major criticism of the Natural Law Theory is that Aquinas presupposes that God created the world and humanity and that they were created for a purpose. There is no proof that God create the world and humanity, but there is a possibility, God is at an epistemic distance, he is close enough for people to believe but too far away for people to know him. According to Bertrand Russell and Richard Dawkins, the universe is random.
Aquinas has based his theory on his experience of the world, not everyone’s. What is Natural?
Aquinas contradicts himself when he says that all humans should reproduce, as he himself was celibate. Many other people have been celibate, for example Mother Teresa; could somebody say that she did wrong?
The natural law theory is an absolutist view on right and wrong. There are alternative ethical theories such as utilitarianism which is a more relativist view and takes consequences into account, as long as the greatest good for the greatest number of people is fulfilled.
There are some advantages of Natural Law. There are clear guidelines and is a fixed moral code, therefore it can be applied universally and Aquinas believed it was innate.
This Divine Command theory is easy to follow as it is centred on human nature and it is deontological so people can make judgements regardless of situation.
When the Natural Law Theory is compared with more relativist ones, it appears to be weaker as it uses objective truths and so what may be considered wrong may have so many benefits, for example an abortion for a rape victim. A relativist would allow the abortion, as they’d understand that the mother may not be able to provide for a child.