Natural Law: Thomas Aquinas a quick summary

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Some facts about him just for your information:

  • Born in 1225; died in 1274
  • Nationality: Italian
  • Educated: University of Paris, University of Naples Federico II
  • His name, Aquinas, comes from the county of Aquino in Italy, where his family held land oHe was a philosopher and a Christian theologian
  • He tried to understand Christianity in light of Aristotle’s rediscovered works
  • He admired, and often cited Aristotle, something for which he was criticized by the head of the Catholic church

He is usually referred to as “Saint” Thomas Aquinas

Why are we interested in him? What does he say about natural law?

His main work, called Summa Theologica, contains the most comprehensive statement of Christian doctrine on the topic of natural law. In terms of time, he comes between Cicero and Finnis so it is interesting to discuss his theory and see how it fits in with theirs. To read more about him, see Raymond Wacks’ book Understanding Jurisprudence at pp 12-15.

There are two main things about his theory that we will examine:

  1. His categories of laws; and
  2. His discussion about the maxim/principle ‘an unjust law is not a law’

1) Aquinas’ 4 categories of law
In his book Summa Theologica, he argued that there are 4 categories of law:

  1. Eternal law: divinereason,knownonlytoGod–God’splanfortheuniverse.1
  2. Natural Law: ‘participation of the eternal law in rational creatures’, discovered by reason – in other words, that part of the eternal law which is known to thehuman mind and is discovered by reason.
  3. Divine Law: revealed in scriptures, Wacks calls it “God’s positive law formankind”.
  4. Human Law: man-made laws, supported by reason, enacted for the commongood. According to Wacks, it is necessary to have the man-made laws to solve many day-to-day problems.

2) His discussion as to whether ‘an unjust law is no law at all’ (les iniusta non est lex)

What is a ‘just law’?

A just law is one that is consistent with the requirements of natural law. It complies with three criteria. First, it is “ordered to the common good”, second, the lawgiver has not exceeded his authority, and third, the laws’ burdens are imposed on citizens fairly. Compliance with those three things makes a law ‘just’. Failure in respect of any of those three criteria would make the law unjust, it would be a ‘perversion of law’.2

Aquinas wrote that unjust laws are acts of violence rather than laws; because… a law that is not just, seems to be no law at all.”3

But the next question is, what is a citizen’s obligations in respect of an ‘unjust law’?

Aquinas adopted the principle that an unjust law is no law at all’ (les iniusta non est lex), although this exact statement is not in his writing. This principle had previously been adopted by Plato, Aristotle, St Augustine and Cicero, but only Cicero and Aquinas really discussed it in depth. Aquinas has become closely associated with it. What does this principle mean?

It seems to be simple enough. It means that if a human-made law conflicts with the requirements of natural law, that law loses its power to bind morally.4

In other words, a government which abuses its authority by enacting laws that are unjust (i.e. unreasonable or against the common interest) forfeits its right to be obeyed because it lacks moral authority. Aquinas would call such a law ‘a corruption of law’. This famous maxim (an unjust law is no law at all) seems to suggest that a citizen does not need to obey an unjust law.

But… wait a moment. Aquinas didn’t mean that a person is always entitled to disobey an unjust law.

Aquinas says that if a government enacts unjust laws, its subjects need not obey them, but he then adds “except, perhaps, in certain special cases when it is a matter of avoiding scandal” (i.e. being a corrupting example to others) or civil disorder. So, he doesn’t really encourage disobedience to law even when it is unjust.

Brian Bix, in his analysis of Aquinas, states that Aquinas meant this: an unjust law is not really a law in the fullest sense. So, such a law does not carry the same moral force as a just law, which is consistent with ‘higher’ natural law. However, Bix thinks that Aquinas did not mean that a citizen could refuse to obey any unjust law.5 Finnis takes the same view.

Natural Law after Aquinas

What happened to natural law after Aquinas? There were a number of scholars after Aquinas who built on his natural law theory. For example, Hugo Grotius (1583-1645) and Samuel Pufendorf. Grotius is sometimes known as ‘the father of international law’ and his writing on international law is based on natural law theory. Grotius famously wrote that even if God did not exist, natural law would have the same content. Wacks explains that statement like this: Grotius regarded certain things as ‘intrinsically wrong’, whether or not they are decreed by God. He once wrote that even God cannot cause two times two not to equal four.6

In the UK, natural law was also popular amongst some legal theorists. In the eighteenth century, Sir William Blackstone referred to natural law when he wrote that English law derived its authority from natural law. Raymond Wacks thinks this was just a way to ‘clothe the positive law with a legitimacy derived from natural law.’7 As we will discuss later, legal positivists such as Bentham criticized natural law as ‘a mere work of fancy’.8

It is important to note that later writing on natural law was usually secular (non- religious). The source of natural law was no longer said to be God. Later Natural Law theorists including Grotius and Finnis referred to “the requirements of reason” rather than the will or wisdom of God as its basis.

    1. See Davies, M. Asking the Law Question (Thomson Lawbook, Sydney, 2008) at pp85-86.
    2. See Bix, B., “Natural Law Theory” in Pattison, D., (ed.) A Companion to Philosophy of Law andLegal Theory 2nd edition (Wiley-Blackwell, UK, 2010) at 213.
    3. Aquinas, 1993, Question 96, Article 4, p.324, as cited in Pattison at 213.
    4. Wacks, R., Philosophy of Law: A Very Short Introduction (Oxford University Press, New York, 2006) at p4.
    5. Bix, B., supra n 2, at 214-215.
    6. See discussion in Wacks, R., Understanding Jurisprudence 3rd edition (Oxford University Press, 2012) at 16.
    7. Ibid at 16-17.
    8. Ibid.


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