1. Introduction

Although the image of the Line is not the best-known analogy in Republic, it is barely noticed that the image of Line is closely relevant to the education of the philosopher king which Plato described. The line is be divided into two sections with different lengths, and continually divide each section into two segments. The first two segments are attributed to the visible realm and correspond to the shadow of the things and the things they are. The first section is illuminated by the sun and produces a shadow to see. However, the shadow is changeable through the variations of the locations or the strength of the sun. The second segment in the visible realm is what we can feel by the five senses and telling the things are practically existing here, and these are what the shadows are. Moving to the later section, the intelligible realm, the first segment account for the whole thing they entirely belong to, which means when referring to a thing, all kind of this thing belongs to one thing it is. Lastly, the second segment of the intelligible world is the principles without any hypothesis and only involve forms.

The first section is illuminated by the sun and then produces a shadow to see. The intelligible world is illuminated by “Good”, which corresponds to the “sun” in the visible form. And for pursuing the terminal purpose of philosopher king, Plato declared, they should take their souls to the Good they are. This can only be done by studying dialectic, which is the most difficult and strict course in the educational system which Plato suggests. Therefore, dialectic seems to become a cardinal skill to be mastered by the philosopher king.

In this paper, we are first going to discuss what is dialectic and dialectical education, and why dialectic is the last course in Plato’s educational system of the philosopher king. After attaining the apprehension of the dialectic in the philosopher king’s education, we will examine why is necessary for the philosopher king to study dialectic, and therefore unravel the intentions of Plato for adding this course.

2. What is the dialectical education?

Let us begin by sketching who is a philosopher king. In the Republic, Plato contends that a philosopher king is indispensable to the emergence and the preservation of the ideal city, i.e., the kallipolis. He is marked by his unparalleled cognitive and practical accomplishments. Only he is able to grasp the Forms the intelligible reality of which perceptible instances of values, such as a just person and a fair transaction, are imperfect images. With that grasp, he alone is able to make and act on sound judgments in day-to-day practical decisions, not only at the personal but also at the political levels. His accomplishments essentially require knowing the Good, the most fundamental Form, which all other Forms, like Beauty and Justice, depend on. The acquisition of that knowledge requires long-standing exercises in dialectics. So, we might be apt to ask: what is dialectics?

In the book of the Republic, Plato believed that the study of dialectics should be the final stage in the process of cultivating the philosopher king. After proposing line metaphors, sun metaphors, and cave metaphors, Plato demonstrated that dialectical education could move from the visible world to the known world, ultimately recognizing the concept of goodness. Plato knew very well what knowledge meant for human growth. In the book "The Republic," Plato wanted to create a learning mode that enabled people to truly understand truth through various aspects such as knowledge, spirit, morality, and so on. Plato's view on the educational model in The Republic. In The Republic, Plato presents his view on the ideal educational model. He believes that education should be focused on the development of the individual's soul and character, rather than just the acquisition of knowledge and skills. Plato suggested that education should begin at a young age, with a focus on physical training and the development of good habits. As children grow older, they should be taught music, poetry, and other arts to cultivate their aesthetic sense and emotional intelligence. In addition, Plato emphasizes the importance of mathematics and philosophy in education, as they help individuals develop critical thinking skills and understand the nature of reality. He also advocates for a system of education that is based on merit, rather than social status or wealth. Overall, Plato's educational model emphasizes the importance of cultivating a well-rounded individual who is capable of critical thinking, emotional intelligence, and moral virtue. Plato believed that dialectical thinking should not perceive the world through sensory perception, only knowledge is rational and objective. Most people only see the surface of things through their own senses. In Plato's view, the difference between hypothesis and dialectic was also discussed. Both are based on the assumption step, but hypothesis will eventually be trapped by various assumptions, while dialectic can enter the next stage and ultimately draw conclusions. Plato also emphasized that the study of dialectics is not suitable for learning at a young age. According to Plato, the philosopher is uniquely suited to engage in dialectic, as they possess a deep understanding of the Forms, or abstract concepts that underlie reality. The philosopher's role is to guide others through the dialectical process and help them arrive at a deeper understanding of reality.

Hugh H. Benson has published an article on Dialectics in the Republic, which argues that dialectics should have a stage of confirmation in addition to the proof stage.

“That is, just as the mathematical method consists of two stages—a proof stage and a confirmation stage, each consisting of an upward and downward path—so does Plato’s recommended method of de novo learning, the method of hypothesis, or dialectic.”

Dialectic is a method of inquiry that involves a back-and-forth exchange of ideas between two or more individuals in order to arrive at a deeper understanding of a particular topic. Through this stage of confirmation, the initial hypothesis can be proven, It is also possible to prove the initial hypothesis through a higher-level hypothesis.

In the book "The Republic", Plato emphasized that the philosopher king should not be allowed to learn dialectics too early and emphasized that dialectical learning was placed in the final stage of the entire process of cultivating the philosopher king. Therefore, it can also be seen that dialectical learning is very important.

3. Why dialectic is the last stage of a philosopher’s educational training?

In the discussion with Glaucon, Plato demonstrated all courses in their order when studying them and emphasizes the reasons why dialectic is the last course can be divided into three perspectives which are the gradually rising dimension of the courses, the evaluation of the philosopher king’s dialectical nature and the unstable character of young people. The education for music, poetry, and speech began in the earliest stage of children’s age to function as shaping their souls. By shaping their soul just, it is limited strictly to offer children good music and poetries. After studying music, as Plato said, gymnastic training becomes easier because a good soul will produce a good body. Therefore, a moderate diet and training from childhood are the primary things they need to do. The purpose of the combination of musical and gymnastic training is to balance the savagery and softness of one when Plato claimed that:

“The man who makes the finest mixture of gymnastic with music and brings them to his soul in the most proper measure is the one of whom we would most correctly say that he is the most perfectly musical and well harmonized” (412a).

These are the rudimentary education for all the citizens in their childhood. After the age of twenty, however, Plato stated more specific courses which the philosopher king needs to study. Mathematics, as the first cardinal subject, has been divided into two sessions——calculation and geometry. Studying calculation after physical training is used to teach people who are dull and insensitive to become acute by practicing and training calculations with numbers, furthermore, makes people apply the apprehension of things to the truth of things. Plato advocated the second course as geometry——from planimetry to the cubes——primarily because it ensures the values in the warfare and military’s strategies and arrangements. If philosophers can extend the soul toward “the region in which lies the happiest things that are” (526e-2), then it is more suitable for studying (There are some more discussions after Plato and Glaucon talked about geometry, which digressed the courses to astronomy. Socrates disagreed to arrange astronomy as a compulsory course because though all the ornamentations in the sky are the most precise things in the visible realm, they are far more different from the truth. Astronomers tend to use sight to evaluate the trace and speed of the decorations in the sky, but the true numbers need to be apprehended by using reason and thought. (529-c7—529-d5) Therefore, the things which can be felt by the five senses are impossible to study their true selves. Additionally, due to the same property shared with astronomy and harmony, the motion detected by ears is also inaccurate). For the last course, Plato proclaimed that dialectic is necessary to be. Dialectic is intelligible, leading souls upward and unable to discard before one truly gets and apprehends good itself. Thus, philosophers must reach “the end of intelligible” (532-b). Plato’s statement emphasized the importance of dialectic when philosophers eventually are led to good. After all, philosophers are coming to the real practice of being compelled to rule as Socrates said:

“Then, at the age of fifty, those who’ve survived the tests and been successful both in practical matters and in the sciences must be led to the goal and compelled to lift the radiant light of their souls to what itself provides light for everything. And once they’ve seen good itself, they must each in turn put the city, its citizens, and themselves in order, using it as their model. Each of them will spend most of his time with philosophy, but, when his turn comes, he must labor in politics and rule for the city’s sake, not as if he were doing something fine, but rather something that has to be done.”(540-a3)

It is worth noting that why people who are qualified for receiving dialectical education must be over the age of thirty, so we might wonder: why young people are unsuitable for studying dialectic?

When mentioning the order of studying, Socrates indicated the incessantly rising dimension of the courses after twenty, and this progressive propelling also leads the philosophers’ soul to the true good which is. As Socrates proclaims that the study of mathematics can only discuss the things that can only be thought about but not be grasped in any other way. Following this choice, mathematics was used to make philosophers easier to see the good that they are. And concentrated solely on geometry, the entire study is for real practice. Although the shapes and objects are continually changing, the terminal purpose is to get the result about recognizing and understanding things, which means geometry is the understanding of what geometry always is. Thereby, until the study of geometry, philosophers’ understanding still extended to the visible real things but did not come to the good which is in the invisible perspective, In the discussion of whether study astronomy, Socrates suggested that:

“The subject dealing with the dimension of depth was next. But because it is in a ridiculous state, I passed it by and spoke of astronomy (which deals with the motion of things having depth) after geometry.” (528-d7)

The main point is to take up the third dimension right after the second(528-b). It seems relevant to the invisible dialectic. However, the cave analogy mentions when people are free to the outside and only observe the shadow in the water, the function of the craft is to lead and rising people to see the brightest things which are visible, for example, the sun. And as those crafts, dialectic also leads philosophers’ souls to the things that they are, rising to the invisible realm. The dimension of depth is revealed by this analogy.

From another angle, Plato deemed that not everyone is suitable for studying dialectic, so there must set some conditions to discover whether people can be inborn dialectical. After the age of twenty, the advanced courses, mathematics, and others will “bring together to form a unified vision of their kinship both with one another and with the nature of that which is”(537-c). For becoming a philosopher king to rule the state, the requirement of dialectical thinking is necessary, which need a unified vision in various aspects for being able to master all of the affairs like military, commerce, and the arrangement of position for different administrators. Also, only this kind of study can link tightly the courses and the nature of a person who is will be illustrated as resolved in all fields to become a philosopher king. Because to have a unified vision is the main standard to evaluate whether one has dialectical nature and can apply the vision to the pursuit of good which is, to reach the world of truth, finishing all the courses before the dialectic and regard the consequences as the criterion to go further in the study of dialectic is reasonable and essential. Aspiring to find resolved one, Socrates said:

“Well, then, you’ll have to look out for the ones who most of all have this ability in them and who also remain steadfast in their studies, in war, and the other activities laid down by law.”(537-c9)

The last point comes to the very unstable and unpredictable character of the young which may turn to evil. Plato explained this by drawing the circumstances of a child. When the child was nourished in a rich family with lots of flatters finds out that he is not the own child of his professed parents while can’t the own parents, Socrates forecasted, the child will lower the homage and enthusiasm of his relatives, get in touch and become more amenable to those flatters. It is similar to the drawbacks of dialectic that if an argument disputes the young about what is beauty or other virtues in diverse ways, the young will turn their soul to the things that are opposing to the just and beauty but contain happiness and don’t regard good virtues as that good. According to this changeable and unstable characteristic, Plato suggests that make those young taste the opposing argument before thirty for playful actions. Then, after the age of thirty, Socrates said:

“But an older person won’t want to take part in such madness. He’ll imitate someone willing to engage in discussion to look for the truth, rather than someone who plays at contradiction for sport.”(539-c4)

In this case, Plato is supposed to study dialectic after thirty which can truly be helpful for them in a mature and steady characteristic to utilizing it correctly. Hence, dialectic naturally comes to the last courses in this progressively educational system which philosophers need to engage in before the practical ruling.

4. The necessity of dialectic in the education of philosopher king

After arguing why dialectics is the last stage of the education of the philosopher-king and represents the completion of the education of the philosopher-king, this section will discuss about what is the intrinsic value of the philosopher kings receiving an education on dialectic and why it is essential. Here are the three fundamental reasons of why dialectic is essential that will be discussed: it makes philosopher kings understand the forms, it can distinguish between opinions and truths, and it provides the state with a clear division of labor.

Dialectic is the only subject to understanding the forms because we cannot access form through our senses or ordinary reasoning. The use dialectic can complement the process of questioning and inquiry so that philosopher kings have a deeper understanding of the forms. Dialectic is the tool for philosopher kings to detach from opinions and reach knowledge; the difference between opinion and knowledge is that opinions are unreliable subjects and sometimes with errors, but knowledge is accurate and reliable [1-3]. One can only understand ethical values using forms, including the understanding of justice, goodness, aesthetic and etc. This is because ethical values are not something that can be observed or touched in the physical world but are abstract concepts that exist in the realm or forms [4, 5]. Understanding the forms gives philosopher kings a privileged grasp of perceptible matters including values and ethics, which would further lead to the ability to distinguish between a just law and an unjust law, and to tell if a person is virtuous or not [3, 5].

“Through education in dialectic and practical city management, some of these people take the final step. They escape the bonds of their spirited desires and are then ruled only by their rational ones. They see “the greatest object of study” (505a), the good itself, and see that it is in some way the cause of all the other things they have seen.”

When encountering the political domain, an inactive or corrupt ruler does not need the education of the dialectic, for they need only to act in their own interest. On the other side, politicians are responsible for appointing and overseeing the people being ruled, the philosophers have a civic duty and responsibility that is instilled in them through their education. Therefore, their education must shape their character and prepare them to govern society in the best possible way [5].

Dialectic can provide the philosopher kings with a dialectical view of things and have no reliance on the senses in processing assumptions [4]. Here we are able to distinguish the difference between dialectic and dianoetic and why dialectic is chosen as the last stage of the education of the philosopher-kings. Dianoetic reasoning can be limited by the biases and assumptions of the individuals involved in the process. While there is certainly value in using logic and analysis, it can also be flawed and distorted if the underlying assumptions or premises are flawed. In contrast, the dialectical method allows for reasoning in a more collaborative and interactive manner, which can help reduce these potential sources of error [3, 4].

“Then also understand that, by the other subsection of the intelligible, I mean that which reason itself grasps by the power of dialectic. It does not consider these hypotheses as first principles but truly as hypotheses— steppingstones to take off from, enabling it to reach the unhypothetical first principle of everything. ”（511 b）

By placing the dialectic in the last step of philosopher king's education can also serve the purpose of filtering out the different types of work in a city-state [3].

“Not everyone is able to take all these steps; there are some at each stage whose desires are too strong for education to break. That is why there are producers (money-lovers), guardians (honor-lovers), and philosopher- kings (wisdom-lovers) in Plato’s ideal city.”

This quote reflects the importance of the dialectic education, that is, to have a clear and essential division of labor in this good city-state, and to filter out the most suitable candidate to be a philosopher-king. The existence of dialectic education not only produces a ruler for the city-state, but also allows the city-state to function, that is, to produce a people whom this ruler can rule and govern [3-5].

In conclusion, the education of dialectic is essential in the education of philosopher king because it makes philosopher kings understand the forms, it can distinguish between opinions and truths, and it provides the state with a clear division of labor. This part has evaluated the importance of dialectic in the education of philosopher king, including its effect and why it cannot be replaced by diagnostic [6-8].

5. Conclusion

In Plato's Republic, dialectic is considered the most difficult and rigorous course in the philosopher-king education system. Dialectic is a method of thinking that emphasizes the recognition and handling of contradictions and opposites. Dialectic education aims to cultivate students' dialectical thinking ability and problem-solving skills. The reason why dialectic is the last course in the philosopher-king education system is that it requires students to have a certain philosophical foundation and thinking ability to understand and apply dialectic. By learning dialectic, philosopher-kings can better understand the world and human nature, solve problems and challenges, and lead and manage society. The internal value of dialectic education for philosopher-kings lies in its ability to help them understand forms, distinguish opinions from truth, and provide clear division of labor for the state. Dialectic education is essential for the philosopher-king education system because it helps to shape the character of philosopher-kings and prepare them to govern society in the best possible way.