In this essay, V. Bradley Lewis gives an introduction to Plato’s philosophy, and its contribution to natural law theory. Although the term “natural law” occurs only once in Plato’s writings, many of his dialogues were designed to call into question the prevailing understanding of nature and law as oppositional. What emerges from Plato is the idea of nature as normative for human affairs as the rule of reason. In his dialogues, Plato suggests that the political art, which is intrinsically legislative, has as its aim the good of the soul of the citizen under its authority. He also suggests that this law can be rationally discerned, while conceding that lawgivers can be mistaken. For Plato, the laws of the city should be guided by a rational and natural ordering of divine and human goods, but discovering the ordering of these goods – and the laws required to promote them – itself depends on reason trained in virtue. In his consideration of the challenges and promises of reason (or intelligence), Plato warns against the dangers that atheism poses to the city, and provides a lengthy natural theology in response. The response serves, on the one hand, to explain the existence of divine souls, but ultimately also the order of goods in the human soul that is of the greatest importance to Plato’s understanding of natural right. By demanding that human laws conform to a natural and rationally discernable standard of justice, Plato helped to initiate a natural law tradition that takes law to be more than a merely arbitrary cultural institution.



Plato was born in 429 BC to a politically powerful Athenian family. He studied philosophy under Socrates, who features as a prominent character in many of Plato’s dialogues. When Socrates died, Plato left Athens to travel; upon returning to Athens, he founded a school called the Academy.

After founding the Academy, Plato reluctantly made two trips to Sicily, both times at the invitation of the dictator Dionysius II, who wanted Plato to teach him to be a philosopher-ruler, as described in Plato’s Republic. Due to political turmoil in Sicily, Plato was held under house arrest until Dionysius permitted him to leave. After returning to Athens for the second time, Plato spent the remaining thirteen years of his life at the Academy, until his death in 347 BC.

Besides Socrates, Plato was also heavily influenced by Heraclitus, Zeno, Parmenides, and the Pythagoreans. Although Plato wrote on a variety of topics, his philosophy is centered on the belief that our world is full of errors, but that philosophy aims to transcend the world of opinion through knowledge of the “forms” or “ideas” of things, sometimes suggesting that those forms are the only reality and that earthly objects merely participate in them. Plato held that men can attain moral superiority by investigating the Forms of the Good, and also believed that the soul is distinct from our material world, pertaining more to the world of the Forms.

To read more about Plato’s life and works, see this encyclopedia article or visit



4th century BC Greek philosopher. He was Plato’s most famous student, and, though he wrote extensively on all topics, is particularly admired for his virtue-based system of ethics. For more information on Aristotle and his relationship to the natural law tradition, please the the section of this website on "Aristotle, Natural Law, and the Founders."  


a popular form of philosophical writing in the classical period in which arguments are advanced through stylized discussion among several characters.

divine goods:

virtues, or goods of the soul: prudence, moderation, justice, and courage. For Plato, these were the most important goods, and just laws would reflect this.


the correct training of one’s passions, aimed at cultivating reason, and, thus, virtue.

external goods:

goods, like wealth, which are external to human beings. Plato believed these to be important, though less so than divine or bodily goods. Laws, to be just, must reflect this hierarchy (or natural ordering) of goods.

human goods:

health, beauty, strength, and wealth in that order. Plato believed that they look to the divine goods, but are less important.

natural theology:

theology based on the rational study of creation rather than on revelation


pertaining to a norm; how things ought to be, rather than simply how they are. Plato believed nature to be normative for human affairs, including the law.


5th century BC Greek philosopher known for his vigorous style of debate in which all beliefs are systematically questioned, and for his unprecedented emphasis on morality as the proper subject for philosophical reflection. He was Plato’s teacher, and features as a prominent character in many of Plato’s dialogues.


an ingrained habit of character that is conducive to living a good life. Plato believed that these habits arise from training one’s passions, which allows for rationality. For Plato, virtue consisted of the resulting consonance between rationality and the properly oriented passions.


for Plato, natural justice is an ordering of goods in which spiritual goods are prioritized, followed by bodily, then external goods. Plato believed this to be in accordance with reason, because it originated in an understanding of man and what is best for him.


the art of public persuasion. Plato believed that rhetoric manipulates the audience by gratifying them, rather than actually seeking the truth. For this reason, he held it to be inferior to the art of politics.


for Plato, the political art was primarily legislative, and aimed at the good of the soul.


the school of thought which takes pleasure as the only good.


the area of philosophy concerned with questions of being.


I.  Introduction – Plato on the natural law

A.     Difficult to gain a systematic understanding of Plato’s thoughts on the natural law

               1.     Only uses the phrase “natural law” once

               2.     Works structured as dialogues, without treatises, in which Plato’s own name is never mentioned. (Socrates often plays the voice of reason)

B.     Plato challenged the existing assumption that nature did not apply to humans; argued that nature was normative, as implied in the Republic

II.             Gorgiason the nature of rhetoric

A.     Socrates suggests that the naturally just is an order of human goods which prioritizes the goods of the soul, followed by those of the body, and then by external goods (e.g. wealth)

               1.     This order is natural because it is rational and integral to human beings

B.     Rhetoric is a merely manipulative art that gives no knowledge of human beings, nor is it good for the soul

C.     The political art is aimed at the good of the soul, and is primarily legislative

D.     Kallikles, the dissenting character, is unconvinced by Socrates’ sound reasoning – a literary device designed to show the limits of rational argument in the face of bad habituation, and thus the necessity of good laws to form good character

III.           Minos – “What is law?"

A.     Socrates says that law “wishes to be the discovery of what is”

B.     Uses analogy of players making different moves in a board game to describe how variations in law still harmonize with reason and permanent structures of the world

C.     Concedes that lawgivers can be mistaken, implying St. Augustine’s thesis that “that which is not right we will no longer say is legal.”

D.     Implies that laws are aimed at the good of the soul

IV.            The Laws – good laws and lawgiving

A.     Dialogue can be divided into three parts:

               1.     Part one contains a theoretical introduction to legislation

i.       Discusses the aims of the city, education, and regime

ii.     One character reveals that he is drawing up laws for a new colony, and the other two agree to assist him

              2.     Part two describes the main features of the city, e.g. geography, government, and education

              3.     Part three discusses resistance to the new city from the three parts of the soul

i.       Desires, especially erotic desires

ii.     Spiritedness as cause and response to crime

iii.    Challenge and promise of intelligence

a.      The dangers posed by atheism, and in response, the longest natural theology of the classical period

B.     Debate centers around what is natural: reason

               1.     Laws should be guided by a rational, natural ordering of goods: bodily, external, divine, and of the soul; all to be placed under intelligence

               2.     Human goods depend on divine goods, and thus on intelligence

               3.     Reason should thus come first and order the city with aid of force

               4.     Virtue is critical to reason

V.              Summary of Plato’s legal philosophy

A.     Justice is ordered towards human goods of the soul, of the body, and of the external world (in that order)

                1.     Since this can be discerned rationally, the law is ordered by reason

B.     Legislation should be just, but lawgivers sometimes err

                1.     Laws are deemed good or bad on the basis of an external and natural standard and are thus not merely a cultural human institution

C.     Good laws are necessary to form good character

               1.     Without good character, individuals in a society are not even capable of using reason, and will thus be unable to discern which laws are good


Part I. Basic Interpretation

If you are interested in the thought of Plato after reading V. Bradley Lewis’s essay, please go to the Primary Source Documents to read some of the essential passages that relate to this article. Please also refer to the biography. As you go back to the primary sources, keep in mind the following questions:

  1. What does Plato think is the purpose of the law? How does he define “law”?
  2. According to Plato, how can men discern the natural law?
  3. How does Plato account for differences in the positive law?
  4. What is the connection between law and virtue?
  5. Why does Plato consider atheism to be so dangerous?

Part II. Connections to Other Thinkers

British philosopher Alfred North Whitehead said that the European philosophical tradition “consists of a series of footnotes to Plato.” Given the enormous influence Plato has had on Western intellectual history, consider how his work fits into the broader history of ideas.

  1. Both Plato and Aristotle believed that some human precepts accord with the natural law and others do not. However, there are some critical differences. How do you think Plato would respond to Aristotle’s idea that, for a precept to be consistent with the natural law, it must be fair? Does Plato’s conception of justice as a proper ordering of human goods imply a different natural law from Aristotle’s? If Aristotle and Plato disagree about the nature of justice, can they agree on the natural law?
  2. In warning against the dangers of atheism in the Laws, Plato clearly holds theism to be central to good citizenship. Consider how theism plays into the natural law thinking of Plato, Aristotle, Cicero, and Aquinas. Is theism necessary for natural law?
  3. Plato seems to think that a man must be virtuous, restrain his passions, and use his reason in order to discern the natural law. How does this compare to Aristotle’s idea about how man discerns the natural law?
  4. Cicero writes: “Not only right and wrong are distinguished by nature, but also in general all honorable and disgraceful things. For nature makes common understandings for us and starts forming them in our minds so that honorable things are based on virtue, disgraceful things on vices” (On Duties). Does this statement accord with Plato’s ideas about how one might discern the natural law? Do Aristotle’s ideas about discerning the natural law through the senses accord with Plato’s?
  5. Consider Plato’s discussion with Kallikles in the Gorgias. There are many similarities between the arguments raised by Kallikles and later arguments made by Thomas Hobbes, particularly in that both suggest that man naturally seeks power for himself. Is Socrates’ argument against this convincing? It didn’t convince Kallikles or Hobbes. Would Plato say that their inability to be convinced was a function of their lack of virtue?
  6. Enlightenment thinkers such as John Locke moved away from an idea of natural law, replacing it with the concept of natural rights. Under such a system, the validity of the law depends on whether it is in accordance with popular sovereignty, rather than in accordance with the natural law. On what grounds might Plato criticize such a view? One might argue that Locke simply had a different conception of justice. Which definition, then, seems more reasonable? And if we have no way of judging, on what grounds can we discern the natural law?
  7. John Adams wrote that the principles of the American Revolution “are the principles of Aristotle and Plato… the principles of nature and eternal reason, the principles on which the whole government over us now stands” (Novanglus, no. 1). However, many of the framers’ ideas were oriented around a Lockean conception of natural rights. Is it possible that the US Constitution might be in accordance with Locke’s ideas and with the more Platonic idea of natural law? Or is there a necessary distinction?

Part III. Critical Interpretations

With a basic understanding of Plato’s thought, let us examine his work more critically. Are his arguments persuasive? Use the following questions as your guide:

  1. Plato argues that good laws are necessary to encourage virtue, but also that virtue is required to discern which laws are good. If virtue and good laws encourage one another, and vice and bad laws encourage one another, then wouldn’t all moderately virtuous nations improve towards excellence with time, while all moderately base ones would decline into depravity? Or are there other independent factors which might affect the quality of laws and the virtue of citizens?
  2. Could Plato’s reasoning be used to justify imperialism? If indeed just laws are more important than the means by which they are implemented, then nations with good laws might be justified in taking over nations with bad laws. Would Plato accept this, or might he suggest that the natural law would forbid such an action?
  3. Plato’s specific conception of natural law seems to depend on a definition of justice as being aimed at a correct ordering of human goods. However, the word “justice” is often used to connote something more like fairness. Is Plato’s use of the word “justice” arbitrary? On what grounds does he make it the basis for his natural law?
  4. Is Plato’s suggestion that the law can encourage virtue in its citizens a plausible one? If so, could the quality of a nation’s laws be measured by the virtue of its citizens?
  5. Plato believed that the good lawgiver was necessarily virtuous, because he believed virtue to be the basis for rationality, and rationality the proper means of knowing the law. However, there are plenty of smart and seemingly rational individuals who would not be considered virtuous by Plato’s definition. Does this disprove his theory? How might Plato address this?

Part IV. Contemporary Connections

Given Plato’s influence on Western intellectual history, it is worth seeing what light his ideas can cast on more contemporary issues. Consider the following questions to examine how Plato’s thinking might interact with our modern world.

  1. Given how important Plato thought it was that citizens believe in some sort of God, can his philosophy be relevant to a secular government like that of the United States? Without having its own religious affiliation or making laws respecting an establishment of religion, might the US government legitimately encourage theistic beliefs in its citizens? Or would this favoritism run counter to the American ideal of religious freedom? It seems like the government would be justified in encouraging patriotism and good citizenship, but if Plato was correct, this could easily extend to fostering religiosity. Was Plato wrong in thinking that a belief in God is necessary to be a good citizen? Even if he was right, is such a factor sufficiently important that the government would be justified in trying to encourage it? Or does allowing the government to take a position on religion constitute too grave a risk?
  2. Is Plato correct in claiming that virtue is necessary to rationally know the natural law and thus to make precepts in accordance with it? If so, what would this mean for the way in which we should elect our legislators?
  3. Typically, the Supreme Court of the United States is comprised of very smart and well-educated individuals. Given the value Plato places on having wise law-givers, might it make sense to give the courts more power, and the democratically elected legislature less power?
  4. Plato’s ideas about how laws ought to be made were based on his understanding of a small Greek city-state. How might his ideas apply differently to a nation as large and complicated as the United States? Or is it possible to combine Platonic legal ideals with something like federalism?
  5. Today, marketing plays a large role in the political campaign process. For Plato, this would likely seem to be more like the art of rhetoric than politics. Such marketing, however, plays an important role in our political process, and has developed out of a legal tradition that values free speech. Given that this is the case, can Platonic ideals be applied to matters of US statesmanship? What might Plato say about our electoral system, and the way individuals behave within it?