Natural Moral Law Revision

By studying our nature and purpose, using reason, we can work out the right way to live.


Philosophical background and context:

Deontological and absolute theory (duty/fixed laws)

Plato’s theory of Forms seems to contribute to the idea of a moral law existing in nature, to be discovered by reason (Form of Good is absolute)

Aristotle: all things have a purpose (final cause). Purpose helps us define action. Two types of justice; conventional and natural.

Stoics; Cicero. ‘True law is right reason in agreement with nature.’


Thomas Aquinas:

13th Century theologian, heavily influenced by Aristotle and Plato.

One of first to apply reason to Christian belief and Christian ethics: 5 Ways and Natural Moral Law.

Assumptions: there is a God, who created the world, there is a soul which must be preserved, we all share the same common nature, we all have the same purpose.


Purpose of life is communion with God; achieved partly by living according to the nature given to us by God.

Our nature can be determined by right reason. (It is possible to misuse reason e.g. Hitler, Eichmann and the Holocaust)

5 Primary Precepts are human nature discovered by reason: this nature is common to us all, so all must live in accordance with it. 5 Precepts are absolute. Pursuing natural law develops virtues.

Natural Law (phusis) is separate from man-made laws (nomos).

Natural Law is general; secondary precepts are specific application of primary precepts.


Synderesis: conscience, all humans naturally tend towards good. Sin results from misuse of reason, pursuing apparent rather than real goods or performing exterior rather than interior acts.


Roman Catholic Ethics.

NML used by R/C Church to decide R/C morality. Carried out by Magisterium and enforced by Pope.

Primary principles applied to produce secondary or remote principles. Known as casuistry: technique of deducing specific rulings by applying general principle (first done in Mark 2:23-28)

Catholic teaching on sexual ethics (e.g. contraception/IVF) arrived at using NML. Genitalia has purpose of reproduction, to use it for any other reason (pleasure/homosexual sex) is morally wrong.

Church teaches that some acts are intrinsically evil e.g. masturbation. (Veritatis Splendour 1993).


Critical analysis of Natural Moral Law: Summary sheet.



Strengths of a deontological/absolute system (Bowie). Provides clear and fixed rules that always apply, removing confusion and exception.

Objective laws, like the 5 precepts apply to everyone.

Common human nature allows us to establish ideas like universal human rights.

Avoids the relativist fallacy (that truth is relative, not absolute; when by its nature, truth is analytically absolute).

Has an empirical basis (in the actual nature of things) and can therefore be verified.

Does not rely on a consideration of consequences, like utilitarianism and situation ethics and therefore avoids calculations and quantities of good/happiness.

Takes account of reason not functioning properly.



When applied strictly, can lead people to do evil things, or permits evil consequences.

Can be said to be counter-intuitive (goes against common sense) e.g. it seems to make sense to endorse contraception in over-populated countries, but NML demands adherence to objective laws.

The existence of objective laws has been challenged by many, including JL Mackie.

The idea that there is a common human nature may be challenged (e.g. homosexuality/disability).

The idea of a common human purpose may be challenged (Aristotle suggested that it could change).

Aquinas’ underlying assumptions (God’s existence/soul etc) may be challenged, removing the ethical motivation and basis for duty.

Proportionalism can be argued to be a better approach (a combination of NML and situation ethics).

Commits the naturalistic fallacy: you cannot get an ought from an is.

Strict NML results in casuistry, which is often seen as a way of introducing exceptions to the rules.

Imposes one purpose upon parts of the human body, when they may have many e.g. procreation and pleasure.


In general, Natural Moral Law is important because it attempts to establish a law that we can all access and which applies to us all (phusis over nomos). This idea is important in human rights law. The Nuremberg Trials, where Nazi death camp officers were tried for their crimes, used the principles of natural law to try them, as the laws of their own country (Nazi Germany) at the time permitted them to do evil.

However, there are serious flaws with the theory, as applying it too strictly does seem to allow people to unintentionally commit evil acts because they are not required to consider the consequences of their actions. Moderate objectivism (proportionalism) may be the solution to this impasse.













About okathleen

I am me - sometimes
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