1. Introduction

This paper has two aims. Firstly, it explains Martin Luther King Jr.’s understanding of just laws. Secondly, it investigates whether King’s account helps to evaluate if a given law is just and ought to be obeyed. It is necessary to highlight that the paper has no intention of comprehensively summarizing King’s view on laws. That would require an in-depth reading of King’s multiple works and an analysis of his actions in the Civil Rights Movement. Instead, this paper narrowly evaluates King’s understanding of laws from his 1963 work Letter from a Birmingham Jail (Letter). Based on Letter, King proposed a law is just if it is moral. The paper will first acknowledge the account's contribution in rejecting segregation laws in the Civil Rights Movement. However, this paper will then argue that King’s account can be theoretically useful as a conceptual instrument when we adopt an abstract interpretation of morality. However, the modified account will be too abstract to be useful in reality.

2. King’s Proposal

In Letter, King argued, “a just law is a man-made code that squares with the moral law or the law of God” (1963: 3). A Law is just when it is moral. King further explained his notion of “moral” by describing it as something (1) “eternal” and “natural”, and (2) respecting human dignity and personality.

King then criticized segregation laws as immoral laws as they were dehumanizing. In support of his criticism, King highlighted two specific concerns. Firstly, the segregation laws were not binding for the white majority. More generally speaking, the laws did not apply to all. Here we can infer that moral law must be fair. It should be unbiased and treat everyone equally. Secondly, the African American community did not have the opportunity to register and vote for their elected representatives and thus, were denied the opportunity to influence segregation laws. The laws were not enacted democratically. This implies a moral law should be non-exploitative. It cannot be a coercive arrangement imposed on the vulnerable groups. 

I categorize the two principles, fairness and non-exploitation, as the auxiliaries for moral laws rather than treating them as separate criteria. This is because the two principles are manifestations of the “moral” criterion described in Letter. Firstly, a moral law must be fair. As the “law of God”, moral laws should be aligned with biblical equality[1], which argues all humans are equal before God “in church, home and society” (Padgett 2002). Also, described by King as "eternal and natural", a moral law is free from human manipulation. It never changes with the will of any individual or society. Secondly, a moral law must be non-exploitative. This is because moral laws “respects human dignity”, while exploitation means treating people as inferior and abusing them politically, economically, or socially.

In summary, based on Letter, King has proposed “being moral” as the criterion for a just law. We have derived two auxiliaries, namely, fairness and non-exploitation, from the “moral” criterion. King put forward a persuasive argument against Alabama’s segregation laws to justify the peaceful protest he led, explicitly highlighting how the laws violated the auxiliaries and therefore the “moral” criterion of a just law.

3. A Good Means to Use?

An important caveat is that King had no intention to generate a rigorous theory of just laws in Letter. Hence, the account that we have derived (with the moral criterion as the core element of just laws and two supplementary auxiliaries) should be labelled as a King-inspired account rather than a King-endorsed account. We will now evaluate whether this King-inspired account is a good conceptual instrument for distinguishing between just laws and unjust laws. If not, we will check whether any modification is possible to improve the account.

In scientific research, it is common to evaluate an instrument from three angles: reliability, validity, and practicality (McClure, Sonak and Suen 1999; Shevchenko and Prokhorova 2017). Reliability is about whether we can reproduce the result in repeated experiments. This attribute is less relevant for our conceptual instrument. Hence, we will evaluate whether King’s account is a “good” instrument based on validity and practicality.

Validity is about whether the instrument measures what we intend to measure. In our context, it is about whether King has provided a plausible content for just laws. I can demonstrate the importance of instrumental validity in another way.

The process of evaluating a given law as just can be summarised as the following.

  1. a law is moral (individual case judgement)
  2. a moral law is a just law (King’s content for just law)
  3. hence, the given law is just.

In order to reach the conclusion III, we must ensure II is true.

Whether II is true largely depends on our interpretation of “moral”. King adopts a theological definition of morality. He equates a moral law with the law of God. His moral law thus narrowly refers to the Christian laws. Even without assessing individual Christian teachings, it is very controversial to argue Christian laws are just laws. With God as the ultimate source of all power, Christian laws are not friendly to non-believers. It is unreasonably restrictive and exclusive to require laws to obey Christian teachings. Many Christians today are unlikely to endorse the idea of adopting theology as the basic of government laws. Christian laws’ metaphysical foundation is simply incompatible with the secular world view. In brief, if we adopt the theological definition of morality, the content requirement for a just law is not plausible.

In order to make II true and generate a potentially good conceptual instrument, we have to abandon King’s theological understanding of morality. We have to find an appropriate secular definition. However, this is not an easy task. The debate on the meaning of morality is not less noisy than the debate on the meaning of justice. Philosophers cannot agree on the nature, source, or contents of morality. A more extreme school, moral nihilism, even rejects the objective existence of morality (Mackie 1990). The contemporary common revulsion against racism means categorizing segregation laws as immoral is acceptable in most moral schools, but harmony disappears if we evaluate more controversial laws such as abortion laws. Therefore, in order to have an inclusive, uncontroversial interpretation of morality, we have to adopt an abstract version. We have to refer to morality as rightness in a very general sense. Taking this notion of morality, King’s account can be instrumentally valid.

Only when the conceptual instrument is valid, the discussion about practicality becomes meaningful. Practicality is about whether the method is useful. In our context, we can evaluate the usefulness from three dimensions.

  1. whether the account includes the sufficient conditions for a just law (sufficient) 
  2. whether the account includes necessary conditions for a just law (necessary) 
  3. hether the account is concrete enough to understand and practice (concrete)

If an account fulfils (1), it is theoretically useful in terms of identifying just laws. If an account fulfils (2), it is theoretically useful in terms of identifying some unjust laws. If an account does not fulfil (3), it will not be useful in reality regardless of the account’s theoretical usefulness. In other words, for an account to be useful in reality, it must fulfil (3) and at least one of (1) and (2). 

King’s main criterion fulfils (1) and (2). By proposing just laws are moral laws, King treated “being moral” as the necessary and sufficient condition for a just law. However, when we try to evaluate (3), the challenge of interpreting “morality” comes back to haunt us. King’s original theological moral law is arguably adequately concrete for practice. When one has sufficient theological knowledge, he or she can evaluate the specific laws in reality with the theological teachings as the guide. In that case, (3) is fulfilled. However, we have rejected the theological moral view as it fails to fulfil the validity condition. We have to adopt the abstract moral view. As the name of “abstract moral view” suggests, it cannot be concrete. Therefore, King’s main criterion is not concrete and therefore not very helpful in reality, even though it can be theoretically useful for identifying just and unjust laws.

The set of auxiliaries of the moral law in Letter is the alternative candidate. It fulfils (2). If a law is unfair or exploitative, exemplified by the segregation laws, it is an immoral and thus unjust law. However, it does not fulfil (1). It fails to mention any theological element so it cannot be sufficient for the theological moral view. Also, it is impossible to comprehensively cover abstract morality in two simple auxiliaries. The set of auxiliaries is insufficient for a moral law in both interpretations. It cannot be sufficient for a just law.

Regarding (3), the auxiliaries are a specification of King’s interpretation of morality and should be better in terms of concreteness. However, they are still not concrete enough for practice. This is evident by the fact that when King used the auxiliaries to reject segregation laws, he had to rely on another level of specification.

  • A law is unfair if it does not apply to all (no universal coverage). 
  • A law is exploitative if it is not democratically voted (no universal suffrage). 

Hence, the set of auxiliaries is theoretically useful to identify some unjust laws but it is not very helpful in reality. 





A just law is a moral law (criterion)


A just law is a fair and non-exploitative law (two auxiliaries)



Given that King has successfully identified the unjust segregation law using the two auxiliaries with the support of the additional layer of specification, some may consider the possibility of permanently adopting the same specification to concretize the auxiliaries. It seems the permanent specification will fulfil (3). As the account then fulfils both (2) and (3), it will fulfil the practicality condition. 

However, this is not a sensible practice. Universal coverage and universal suffrage are necessary rather than sufficient conditions for the two auxiliaries. In other words, they are not comprehensive concretization of the auxiliaries. They merely rule out some unfair and exploitative features. If a law applies to all, it may not be fair. For example, the policy of free university education for all fulfils the requirement of universal coverage, but it is not necessarily a fair policy (O’Malley 2015; Baum and Turner 2019). Children with a wealthier family background are more likely to be admitted to universities. Hence, they enjoy a larger share of the policy benefits than their poorer counterparts. Also, even if a law is democratically voted on, it may not be non-exploitative. People’s voting decisions can be shaped by exploitations in the form of coercion, education deprivation or even brainwashing. When the house-elves in Harry Potter were given the chance to get paid and be free, they expressed great disgust and unwillingness. They sincerely believed they were born servants of humans. They would love to be “voluntary slaves”. I am not only talking about novels. Abusive social culture can influence the self-evaluation of the exploited and their children. Females living in a male-dominated society, and Dalits at the bottom of the Hindu caste system are both real-life victims. In summary, if we choose to make the auxiliaries more concrete by embedding these additional specifications in the account, we will further narrow the applicability of the account. It will only become useful in identifying a small group of unfair and exploitative unjust laws in the specific form of failing to provide universal coverage or suffrage. Many other unfair and exploitative laws will not be detected. 

4. Conclusion

In conclusion, a modified[2] King-inspired account of just laws can be a theoretically useful conceptual instrument to identify unjust laws. However, it is too abstract to be useful in reality. Nonetheless, there can be reasons for optimism. There is no need to use King’s account independently. If there can be convincing context- and case-specific concretization of the moral criterion and its auxiliaries (like what King did in his analysis of segregation laws), the account can be greatly beneficial. This is where philosophers and legal practitioners can make a huge difference.


I want to thank Dr Liam Kofi Bright for the supervision, encouragements and constructive feedbacks. I also want to thank Professor Alex Voorhoeve and my PPE peers for creating a stimulating academic environment for discussions and debates. Also, I greatly appreciate my family for creating an extraordinarily conducive environment so that I can focus on my studies. Last but not least, I want to thank my friend and colleague Kitty Rae Thompson and Lewis Humphreys for proofreading this paper.


[1] King’s “God” should refer to the Christian God.

[2] In terms of interpreting morality in a general, non-theological sense.


Baum, S. and S. Turner. 2019. ‘Free tuition’ is the Opposite of Progressive Policymaking. [online] The Washington Post. URL

King, M.L, Jr. 1963. Letter from Birmingham Jail [Ebook]. URL

Mackie, J. 1990. Ethics: Inventing right and wrong. Penguin UK.

McClure, J.R., B, Sonak and H.K. Suen. 1999. Concept Map Assessment of Classroom Learning: Reliability, Validity, and Logistical Practicality. Journal of Research in Science Teaching: The Official Journal of the National Association for Research in Science Teaching36(4), 475-492.

O’Malley, B. 2015. Free higher education is ‘regressive’ – World Bank. [online] University World News. URL

Padgett, A.G. 2002. What is Biblical Equality? A Simple Definition Needs Further Discussion, not Least because of Misunderstanding. Priscilla Papers.

Shevchenko, S., and E. Prokhorova. 2017. Standard Setting: Validity, Reliability, Practicality. 45th International Philological Conference (IPC 2016),484--487. Atlantis Press.