The primary precepts are aspects of life and things that we naturally seek to fulfil as humans. They are as follows: preservation of life, living in an ordered society, worshipping God, education, and reproduction. So for example, killing someone is always wrong because it goes against the precept of preserving life.
Secondary precepts are deontological absolute rules derived from the primary precepts. For example, the secondary precept of preserving life would be not to kill, and the secondary precept of worshipping God would be to go to church every Sunday. So even in the case of suicide, it is wrong because killing yourself would go against preserving life. The Catholic Church uses Natural Law. Catholics are not allowed to use contraception. This is because using contraception is not a secondary precept of reproduction, it goes against it.
An aspect of Natural Law theory which allows for some flexibility is the Doctrine of Double Effect. This states that as long as breaking a primary precept is not an intended effect of an action, it is acceptable. The example I will use to explain this is an ectopic pregnancy. In an ectopic pregnancy, both the life of the foetus and the woman will end if the pregnancy is allowed to run its course. For a follower of Natural Law even in this circumstance, performing an abortion would be wrong even though it would save the mother’s life and still allow her the ability to get pregnant in the future. However the doctrine of double effect would allow for the doctor to remove the fallopian tube and ovary with the unintended side effect of ending the life of the foetus. This is an acceptable act as the intentions are not evil, the ending of a life is not intended by the doctor.
In conclusion the Natural Law theory was written by Thomas Aquinas. Aquinas was a 13th century monk who studied Aristotle’s four courses. He used the idea of the final cause, or purpose to come up with 5 things that humans need to do in order to fulfil their purpose. He called these the primary precepts. Secondary precepts are absolute laws that are derived from the primary precepts. Although the theory is absolute, the doctrine of double effect allows for some flexibility in certain individual circumstances.