The arc of the moral universe
A brief philosophical journey to 1776
In his final sermon before he was murdered, Martin Luther King said,
"We shall overcome because the arc of the moral universe is long, but it bends toward justice."
This is a beautiful sentiment. It has been repeated many times since. Like most thinkers, King was paraphrasing this thought from a previous minister. His name was Theodore Parker and he was a Unitarian minister and abolitionist. He lived from 1810-1860, roughly 100 years before King. Here is his version:
“I do not pretend to understand the moral universe; the arc is a long one, my eye reaches but little ways; I cannot calculate the curve and complete the figure by the experience of sight; I can divine it by conscience. And from what I see I am sure it bends toward justice.”
I don’t cite this to take anything away from King. In fact, until I was preparing to write this post, I thought that this was King’s original rhetoric. I discovered Parker while I was looking for a copy of King’s speech. The fact that King drew on Parker helps make a point I was looking to make today: philosophical perspectives grow slowly over time and through eras, building on what was said and thought in previous generations. There is no Athena-like springing, fully grown, from the head of a god. As a result, good people struggle along the arc of justice, seeking to make the world more free, more kind, more beautiful.
July 4th, Independence Day for the United States of America, was the day before yesterday. I wrote last year about the spiral of inclusion, and about how the systems put in place by the Founders have been working, arcing outward, to include more an more people. The words penned by Thomas Jefferson,
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness…
did not emerge, fully formed, in a sweaty Philadelphia without precedent. Indeed, he was paraphrasing John Locke, who wrote in 1689, about 100 years earlier:
The end of law is not to abolish or restrain, but to preserve and enlarge freedom. For in all the states of created beings capable of laws, where there is no law, there is no freedom…
For liberty is to be free from restraint and violence from others, which cannot be where there is no law…
The reason why men enter into society, is the preservation of their property; and the end why they choose and authorize a legislative, is that there may be laws made, and rules set, as guards and fences to the properties of all the members of the society…
[including] their lives, liberties, and estates, which I call by the general name, property.[1]
Locke is typically quoted as being for life, liberty, and property, only one word off from Jefferson. Locke was interested in the conditions that enable human flourishing, which I think Jefferson would have agreed is what he meant by “happiness” – eudaimonia, not hedonia (see my previous post “The "H" in "Army" stands for happiness” for more on the difference).
King was right, Parker was right: the United States has been on a trajectory of greater justice for hundreds of years. It continues to do so because of natural law. Natural law theory emerged in the West in Classical Antiquity (500BCE to 300 CE), from the Greeks and Romans. The idea was that the universe has a certain logic to it, and that we should live in harmony with it. This logic extends to human affairs, not just the physical. If we could perfect our understanding of natural law, we could perfect human affairs. Unfortunately, as is typical of our species, they took for granted that their current arrangements – class hierarchies, including slavery – were the natural order. But the seeds of freedom and equality were born out of this understanding. Natural law dictated that full citizens (male, property owners) had certain rights.
Christian theology blended with Roman law in Late Antiquity (about 300 CE-800 CE) to introduce that idea that all human souls had equal worth before God, and this idea suggests all humans have value, regardless of status. Indeed, Christianity has always played with the idea of an inverted hierarchy (“The last shall be first” – Matthew 20:16). It’s a long way from the Bill of Rights, but we have to start somewhere.
In the Medieval Era (800 CE – 1300 CE), philosophers worked to more fully integrate Christian doctrine with Classical texts (in particular Aristotle), and to weave faith and reason together. Thinkers such as Thomas Aquinas integrated natural law and theology, arguing that all humans have reason, and therefore naturally have moral rights and duties. This argument is important in getting to human rights.
Much of Aquinas’s work was integrating classical philosophers, especially Aristotle, but the Renaissance (1300-1600) was a broader integration of classical philosophy into the culture. Humanism emerges, along with secular learning. Not everything is seen through a theological lens. Renaissance humanism emphasizes human dignity, individual moral agency, and the worth of human achievement.
The late Renaissance sees two major social events:
1) Reformation (1517-1648): In 1517, Martin Luther posts his 95 Theses, challenging the authority of the Catholic Church. This ignites religious and secular reform in Europe. In 1648 we have the Treaty of Westphalia, where the great powers agree to stop killing each other over religious differences. At least on large scale. It also helps establish some basics of international law, and recognition of national states.
2) Scientific Revolution (1543-1700): A new (or reborn) way of knowing, based on empirical observation rather than revelation or theory. This becomes possible because of the Renaissance break with seeing through a theological lens. The scientific revolution extends from the physical to the social.
Each era builds on the prior. Aquinas integrated his inheritance of early Christian thought and integrates it with Antiquity. The Renaissance catches fire as the ideas of Antiquity are extended beyond theology. The Reformation and Scientific Revolution are possible because of the possibility of skepticism introduced by the Renaissance. And that leads to the Enlightenment, in the late 1680s, when Locke’s ideas about individual rights and the purpose of government emerge, the Glorious Revolution in establishes a constitutional monarchy in Great Britain, and Newton’s Prinicipia Mathematica is published, providing a model of a rational, natural order that the Greeks could only theorize about. The Enlightenment was a movement that brought to fruition the idea that governments exist to serve the people, not the other way around, and they exist to protect the rights of individuals, not just the elite.
It's about a hundred years into the Enlightenment that some backwater colonies far from the center of Western Civilization publish what proves to be one of the great statements of human history – that all men are created equal and have unalienable rights. But it couldn’t have happened independently. It had to come after some two thousand years of intellectual development. As Parker said, my eye reaches but little ways when I try to look forward, but it is easy to look backward (especially with ChatGPT!). It’s appropriate to be dissatisfied with where we are – we should always be looking to perfect our concordance with natural law. But on July 4th, 2025, it is appropriate to celebrate how far we have come, and to honor the efforts of all those who pledged their lives, fortunes, and sacred honor to get us here.
The United States has assured more people have more freedom than any other country ever in the history of the world. It’s up to us to celebrate and protect our inheritance, because none of this emerged fully formed, and because the arc bends slowly and not consistently in all places and all times.
God bless America.
[1] Locke, J. (1689/1980). Second Treatise of Government (C. B. Macpherson, Ed.). Hackett Publishing Company. (§87)
The following is the ChatGPT output I used to help draft this post. It’s such a great research assistant.
Classical Antiquity
600 BCE – 500 CE
Reason, natural philosophy, civic virtue, metaphysics
Introduced the concepts of natural law, civic participation, and justice. Athenian democracy and Roman legalism laid groundwork for later ideas of legal equality and citizenship—though limited to male elites.
Late Antiquity & Early Christian Thought
300 – 800 CE
Christian theology, salvation, synthesis of classical and religious thought
Introduced the idea of the equal worth of all souls before God, planting moral roots for equality. Christian universality promoted the belief that all people have value, regardless of status.
Medieval / Scholastic Era
800 – 1300s
Faith and reason, divine order, theology as queen of sciences
Thinkers like Aquinas advanced natural law theory, arguing that moral truths are accessible through reason to all people, implying a shared human nature and rights derived from it.
Renaissance
1300 – 1600
Humanism, revival of classical texts, secular learning, individual potential
Emphasized human dignity, secular achievement, and the moral agency of individuals. This helped shift authority from divine order to human reasoning—essential for asserting individual autonomy.
Reformation
1517 – 1648
Religious reform, personal conscience, challenge to Church authority
Asserted the right of personal belief and private conscience, promoting freedom of religion, individual responsibility, and anti-authoritarianism—cornerstones of future civil rights.
Scientific Revolution
1543 – 1700
Empiricism, observation, natural laws, mathematical modeling
Created a belief in universal human reason and shared capacities, legitimizing the idea that rights could be based on rational, observable human nature, rather than divine or monarchic decree.
Enlightenment
1685 – 1815
Reason, liberty, progress, secularism, universal rights
Synthesized prior ideas into a political philosophy of natural rights (life, liberty, property), universal human dignity, democracy, tolerance, and equality under law. Influenced revolutions and declarations (e.g., U.S. Declaration of Independence, French Declaration of the Rights of Man).