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Plato’s Philosophy – Summary

PLATO (428-348 b.C.)

Summary of his thought


School of Athens

(detail: Plato)

 Rafael – 1509-1510

I. The Theory of the Ideas and plato’S ontology

I. 1. Theontological dualism

I. 2. Plato’s arguments in favour of the Theory of the Ideas





V.1. The virtue

V.2. The king-philosopher

V.3.The «platonic Communism»

Plato– In A Brief History of Greek Philosophy – by B. C. Burt.


I. 1. The ontological dualism

       The theory of the Ideas is the base of Plato’s philosophy: the Ideas are not only the real objects ontologically speaking, but they are the authentically objects of knowledge epistemologically speaking. From  the point of view  of ethics and  politics,  they are the foundation of  the right behaviour,  and anthropologically speaking they are  the base  of Plato’s dualism and they even allow him demonstrate  the immortality of  the soul.

Plato defends a clear ontological dualism in which there are two types of realities or worlds:  the sensible world and the intelligible world or, as he calls it, the world of the Ideas. The Sensible World is the world of individual realities, and so is multiple and constantly changing, is the world of generation and destruction; is the realm of the sensible, material, temporal and space things. On the contrary, the Intelligible World is the world of the universal, eternal and invisible realities called Ideas (or «Forms«), which are immutable and do not change because they are not material, temporal or space. Ideas can be understood and known; they are the authentic reality. The Ideas or Forms are not just concepts or psychic events of our minds; they do exist as objective and independent beings out of our consciences. They are also the origin of sensible things, but although they are the authentic beings, Plato, unlike Parmenides of Elea, do not completely deny the reality of the sensible things; the sensible world, although ontologically inferior, have also certain kind of being which comes from its participation or imitation of the world of Forms.  The task of Demiurge is to give the shape of the Forms to that shapeless sensible material that has always existed making it thus similar to the Ideas.

The Ideas are hierarchically ordered; there are different types and they do not have all the same value. The coherency of the arguments Plato uses for defending the existence of the Ideas would have lead him to claim there are Ideas of all those general words of which we can find an example in the sensible world, that is to say, of all the universal terms such as «justice», «rightness» or «man», but also terms as «table», «hair» or «mud». In spite of it, the population of Ideas postulated by Plato is limited enough by value considerations. Sorts of Ideas that are included in the intelligible world: the Idea of Rightness and other moral Ideas (Justice, Virtue, etc.); Aesthetic Ideas (specially the Idea of Beauty), Ideas of Multiplicity, Unity, Identity, Difference, Being, Not being, mathematical Ideas and other Ideas (the Idea of Man, etc.).  Plato locates the Idea of Rightness on the highest position of that intelligible world; sometimes he identifies it with the Idea of Beauty and even with the idea of God. The Idea of Rightness is the origin of the existence of everything because human behaviour depends on it and everything tends to it (intrinsic purpose in the nature).  


I. 2. Plato’s arguments in favour of the Theory of the Ideas

       In essence, this theory defends there are certain independent, universal, immutable and absolute beings which are different from the sensible world.

a)  Critic of the sensible knowledge in the dialogue «Theaetetus»: Plato shows evidence does not rise from sensible knowledge. This kind of knowledge leads to relativism, which is, in essence, absurd (critic of sophist philosophy). Besides, we have knowledge not based on the senses. Conclusion: science (knowledge strictly talking) based on sensation as criterion for truth is not possible, because we cannot have science of changeable things (of the sensible world) which just appears to our senses. Science has to be based on reason, which studies the nature or essence of things («Ideas»).

b)  The use of the language and the problem of the reference of the universal terms. Linguistic terms as nouns («table»), adjectives («good») and abstract nouns («beauty») of which many examples can be shown lead to think about the existence of beings different from the individual and sensible ones. The objects to which names (such as «Socrates» or «Napoleon») refer are individuals; but we have certain problems about the objects to which other terms (nouns, abstract adjectives and abstract nouns) refer. We call them UNIVERSAL terms because they do refer to a plurality of objects. For that reason Plato deduces there must be universal beings matching up those universal concepts of which there are plenty of individuals or examples; “The Green” would match the concept of «green», “The Kindness” would match the concept of «kindness», “The Beauty” would match the concept of «beautiful», “The Truth” would match the concept of «truth». Those beings which match universal concepts are called Ideas or Forms.

c) The possibility of scientific knowledge: science strictly talking cannot deal with things which are continuously changing; the sensible world is continuously changing, so science cannot study it; it has to study an immutable world. The second premise shows a clear affinity with Parmenides of Elea and Heraclitus of Ephesus: what is given to our senses is a world ruled by continuous change, by mutation. As far as the first premise, we have to think about something permanent in those objects we want to have knowledge about if we want this knowledge to be true. Is there any knowledge that is always true and not just sometimes true?  If there is, then we have to think there are things that don’t change and our knowledge will have to refer to them. Plato thinks MATHEMATICS is immutable. The science he is looking for will have to be universal and will have to be based on reason exactly as mathematics. Plato thinks that kind of knowledge is possible referring to a realm of real things different from the mathematician; and both disciplines (mathematics and that superior knowledge he calls «dialectic«) will be strict knowledge because they refer to immutable objects. These immutable objects are the «Ideas».


        In the VII book of the «Republic» Plato displays his well-known myth of the cavern, the most important one as it embraces the cardinal points of his philosophy. He wants it to be a metaphor «of our nature regarding its education and its lack of education», that is, serves to illustrate issues regarding the theory of knowledge. Nevertheless, he clearly knows this myth has important consequences for other fields of philosophy as ontology, anthropology and even policy and ethics; some philosophers have seen even religious implications.  The myth describes our situation regarding knowledge: we are like the prisoners of a cavern who only see the shades of the objects and so live in complete ignorance worrying about what is offered to our senses. Only philosophy can release us and allow us come out of the cavern to the true world or World of the Ideas.

Plato requests us to imagine we are prisoners in an underground cavern. We are chained and immobilized since childhood in such a way we can only see the far end wall of the cavern. Behind us and elevated there is a fire that lights the cavern; between the fire and the prisoners there is a path on which edge there is another wall. This second wall is like a screen used in a puppet theatre; puppets are raised over it to be shown to the public. People walk along the path speaking and carrying sculptures that represent different objects (animals, trees, artificial objects…). Since there is this second wall between the prisoners and the people walking, we only see the shades of the objects they carry projected on the far end wall of the cavern. Naturally, the prisoners would think the shades and the echoes of the voices they hear are true reality.

Plato argues a liberated prisoner would slowly discover different levels of authentic reality: first he would see the objects and the light inside the cavern, later he would come out of it and see first the shades of the objects, then the reflections of those objects on the water and finally the real objects. At last he would see the Sun and conclude it is the reason of the seasons, it rules the realm of visible objects and is the reason of everything the prisoners see. And remembering his life in the cavern, remembering what he thought he knew there and his captivity comrades he would feel happy for being free and would feel sorry them; prisoner’s life would seem unbearable for him. But in spite of it and in spite of the dangers, his clumsiness and the prisoner’s laughs and scorns, he would return to the underground world to free them.

These are the keys Plato gives us to read the myth: we should compare the shadows of the cavern with the sensible world and the light of the fire with the power of the Sun. The escape to the outer world to contemplate real beings (metaphor of the World of the Ideas) should be compared with the path our souls take towards the intelligible world. Plato declares the most difficult and the last object we reach is the Idea of Rightness (symbolized by the metaphor of the Sun, the last object the released prisoner sees), which is the reason of all the good and beautiful things of the world; it is also the reason of the light and the Sun in the sensible and visible world and the reason of truth and understanding in the intelligible world; is the reality we need see to live with wisdom.


      The theory of the Ideas answers the question about the possibility of knowledge strictly talking.  This theory divides the world in two realms of reality completely different ontologically speaking which will match two different wisdoms. Types of knowledge: SCIENCE; which take care of the immutable Ideas and is divided in dialectic and discursive thought and OPINION; which is the knowledge of the sensible and changeable world and is divided in belief (which occupies on the «animals surrounding us, plants and the whole of artificial objects) and conjectures (which occupies on «shades» and similar things).

Plato distinguishes between discursive thought and dialectic in what he calls SCIENCE. The first one is mainly identified with mathematics (geometry and arithmetic), and in spite of its extraordinary value, it has two important deficiencies: it uses sensible symbols and leans on hypothesis (careful; «hypothesis» in Plato’s philosophy does not mean the same as for us): mathematicians do not reflect on the being of the objects they deal with (the numbers, for example) nor settle down any thesis ontologically speaking, and that’s why this science is incomplete. Dialecticis a superior knowledge, studies the World of the Ideas, that is to say, the immutable, universal and eternal being, and is identified with philosophy. Plato conceives it in two ways: as a rational method which uses only the reason but not sensible symbols, nor rest upon «hypothesis», trying to do without assumptions; philosophy (=dialectic) is the most reflective knowledge, the most comprehensive as it does not leave any question without examination; its purpose is to discover the relations between the Ideas and to find out the ultimate foundation of them all in the Idea of Good. Authentic philosophy is «a way up to being«: the philosopher has to pass from the sensible world to the world of the Ideas and from these to the Idea that rules knowledge and being, that is, the Idea of Rightness or Good (remember the metaphor of the cavern and the liberated prisoner; his vital experience is analogous to the philosopher’s: the prisoner comes up to the outer world and discovers the Sun is the reason of the being and the intelligibility of things; the philosopher (the dialectic one) passes from his experience in the Sensible World to the Intelligible World where he finds the Idea of Good as the foundation of the being and the intelligibility of the Ideas and the sensible reality). But Plato also understands dialectic as a yearning impulse: the philosopher ascends from the sensible to the intelligible level; this ascent is not only intellectual, and it does not end with the Idea of the Good, but with the Idea of Beauty. The motor of this ascent is the yearning impulse and the object of this yearning (Eros) is beauty.


         The ontological dualism «sensible/intelligible world» matches Plato’s anthropological conception of human being clearly divided in body and soul (anthropological dualism).  Plato conceives man as a compound of two different substances: the body, which ties us to the sensible world and the soul, which removes us from this material sphere and relates us to a superior world. Human soul is understood as immortal and it has a superior destiny than the body. This superiority comes from the fact that the soul (contrary to the body) is, in essence, a rightness and knowledge principle and moreover, the body is ruled by corruption and death whereas the soul is immortal. Plato uses several arguments to demonstrate the immortality of the soul, emphasizing the one that rests on the reminiscence theory: in his dialogue titled «Meno», Plato defends the thesis that TO KNOW is TO REMEMBER: we do not have a genuine knowledge experience (of the universal being): when we say a mathematical proposition is true, it is not because we have just learned it, but rather because we remember the relations between the Ideas our soul knew in  the world of  the Ideas before incarnating in  our body. The perception of the sensible world cannot serve as foundation for strict knowledge but, since we have such knowledge, it must come from a previous experience. Therefore: to know is to update a knowledge already experienced, to know is to remember (this thesis is called THEORY OF the REMINISCENCE).

Like all ancient Greeks, Plato defends the soul is a principle of movement in itself and a movement source. But the singularity of his conception is the soul distinguishes itself from the body in a relevant feature: it makes us equal to Gods and allows us to know the Ideas. Plato distinguishes three elements or functions in the human soul: the rational element, which is represented in the myth of the winged carriage by the coachman, is the most dignified and elevated; its functions are the intellectual knowledge and the direction and guide of the other two; the irascible element (quick tempered), represented by the good and beautiful horse, symbol of the strength and the Will, which is easily leaded; and the concupiscent element (immoderate or hot-headed), represented by the bad horse, hard to guide, which symbolizes the immoderate desire and sensible  passions. The soul seeks its freedom from the body and practices philosophy as an intellectual approach to the world it authentically belongs to. The rational element of the soul must try to purify the individual from his sensible desires and that’s why it has got the ruling role of human behaviour.

Plato’s anthropological dualism is characterized by a radical split in human being: following the Orphic doctrine, Plato declares there are two principles in human being: the immortal SOUL, our most divine part, principle of knowledge and morals; and the BODY, the reason of our ignorance and our wrongness. Plato begins the Western traditional thought for which the body and its   passions are the main responsible for all our pains, misfortunes and sufferings; man is guilty simply because he has a body, idea particularly dear for Christianity. Therefore, our most important tasks will be, on the first place, the practice of virtue, which means basically to sacrifice body desires, and secondly the practice of philosophy. The purpose of moral and intellectual purification is to let the souls be guided by rightness and straightness and thus fulfil their fundamental destiny: those who practice philosophy and so know the world of the Ideas will return to their original place (the divine dwelling), where they lived before; on the contrary, the impure ones, those who let their uncontrolled passions rule their behaviour will have to undergo a judgment and will be condemned to wander an mistake indefinitely, paying thus their faults in life.


a) The virtue  The theory of the Ideas implies the overcoming of the sophistic moral relativism: the Ideas of Justice and Rightness become the perfect criteria for distinguishing right from wrong or fair from unfair. The Ideas are values themselves. Plato’s ethics tries to find out what is the Highest Rightness for man, Rightness whose attainment implies happiness and which is achieved by the practice of virtue. The Highest Rightness can be understood in two ways: a good life cannot be achieved neither by the only means of moderate pleasures nor by the only means of wisdom, but by a mixture of both, simply because man is a mixture of animal and intelligence. (Of course, the pleasures we can indulge in are the purest ones). According other philosophers, Plato’s Highest Rightness means contemplating the Ideas, contemplation which is the supreme happiness. In this sense the virtue, as the method for achieving the Highest Rightness, performs an analogous roll as dialectic, the method for achieving the Intelligible World. By means of the practice of virtue we achieve the Highest Rightness and, therefore, the supreme happiness; virtue is the natural disposition for rightness of our souls, and as our souls have three elements, there will be three peculiar virtues, one for each one of them: self-control for the concupiscent element: «certain order and moderation of the pleasures»; strength or braveness for the irascible element: the strength allows man surpasses suffering and sacrifices pleasures if necessary; and wisdom or prudence for the rational element, which rules the whole human behaviour.  The virtue of the soul as a whole is justice, which settles order and harmony between those three elements and is, obviously, the most important virtue. Along with this practical explanation of virtue Plato defends a more intellectual theory particularly related with the theory of the Ideas: virtue is the knowledge of what is right for man or, better, the knowledge of the Idea of Rightness, and is mainly identified with wisdom or prudence. We should remember the Ideas allow Plato surpasses the moral relativism of the sophists as the Idea of Rightness implies there is an absolute point of view.

b) The king-philosopher As every Greek, Plato thinks man is naturally a social being; that’s why there are States (Polis). The individual can reach his utmost accomplishment in the State, but only in a perfect State. Plato divides the State or society in three classes following the three elements of the soul; the State is a great organism with the same material and immaterial requirements and ethical aims as man. The rational element of the soul is represented by the class of the governors, who are philosophers; the irascible element is represented by the social class of the soldiers; the concupiscent element by the craftsmenThe philosophers, whose particular virtue is wisdom or prudence, are the only ones capable for government; the soldiers, whose virtue is the strength, must defend and keep safe the polis; the craftsmen, whose virtue is self-control, provide the commodities needed in the State. Thus, a total parallelism between anthropology, ethics and policy is settled down. The three social classes are needed, but each one enjoys different rank and dignity. The aim of the State is justice: the common welfare of all the citizens, which would only be possible if every class fulfil its own roll. Plato distinguishes the social class of the leaders: since the Idea of Rightness can be known, it’s only natural philosophers guide society ruled by their superior knowledge; philosophers have to be governors or governors have to be philosophers; of course, philosophers do not seek their own interests but the community’s.

c) The «platonic Communism» Philosophers must seek the general welfare and so, trying to avoid temptations and useless distractions, they neither have private property nor family; their main purpose is wisdom which enables them to carry out their mission of government. Soldiers also sacrifice family and private property, only the craftsmen are allowed to them (though limited and controlled by the State).  Craftsmen do not need education, except the professional for their own tasks, and they must obey political powers. In this ideal State only a very best selected minority have power. Though the social classes are not closed up, social mobility is controlled by rigorous criterion. Plato’s ideal State is clearly aristocratic. Finally, along with this description of the ideal society, Plato describes and assesses the actual forms of government: there are five, but they all come from the monarchy or aristocracy by progressive decay: military dictatorship, oligarchy, democracy and, the worse of all, tyranny. Monarchy or aristocracy is the most perfect form of government: is the government of the best individuals.

©Javier Echegoyen Olleta –  translated byIsabel Blanco González