Philosophy is a subject that can take many twists and turns before it finds an answer to a general question. Sometimes, an answer is still left unfound. Philosophy, in its broadest terms, can be described as the systematic pursuit of knowledge and human excellence. What we are concerned with is knowledge. Many people have theories of knowledge. Amongst them, there are two we will be looking at, Descartes and Plato. We will examine Descartes' epistemology in Meditations on First Philosophy and Plato's in The Republic.
Descartes' epistemology is known as foundationalism. In the Meditations, Descartes doubts everything he was taught to believe because it is human tendency to believe what is false. In the first, he claims that most of what he believes is from his senses and that those senses are sometimes deceived. His solution to doubting everything is compared to a basket of apples. You fear that some apples have gone bad and you don't want the others to rot, so you throw all the apples out of the basket. Once this is done, you examine each one and return the good apples to the basket. This is what he does with his beliefs. He keeps only those he is certain of. We must discard our beliefs as a whole and then examine each one individually. We must build on the good beliefs. Descartes, however, does realize we can't throw every belief out because they are a part of us, unlike the apples. We would have no basis for recovering any of our beliefs. We would be unable to justify anything. No belief based on sense-perception is free from doubt. He said it is possible that his life is all a dream and he is being deceived into thinking it is reality. He also holds false anything that is physical exists, including his own body. The only things we should trust are those beliefs that are subject to rational scrutiny. We must also declare our mathematical judgments to be false also because an evil demon might be deceiving us. Now, Descartes has cast doubt on all his beliefs about everything but himself. He cannot be deceived about himself. It is on himself that he will be able to rebuild his knowledge of other things. If he had no knowledge of himself, then nothing can be certain. If he doubts, he must be an existing self which is engaged in doubting. If he doubts, he must also be thinking and Descartes said " I think, therefore I am." He must also exist so that he can be deceived. If he is dreaming, then he is also thinking, thus he still exists. This is the first step to acquiring knowledge, to Descartes. You must build on what you know is certain, starting with yourself as the foundation.
In the second meditation, Descartes tries to show we know bodies through reason and not through senses. He uses a piece of wax to demonstrate. Over a period of time, a freshly produced piece of wax placed by the fire loses or changes all its specific properties, yet it is known to be the same object. Its taste and odor disappear. Its color, size, and shape are completely transformed. It loses its hardness and coldness to liquidity and warmth. To know the wax, you must be able to anticipate its changes. Descartes argues, though, that the imagination could not possibly figure out all conditions, for they are infinite. One can only know an object through understanding, rather than through images, sensation or imagination. He now has knowledge about himself and any object that he has thought about through reason. We are now moving along nicely in rebuilding our house of knowledge.
In the third meditation, we move into another building block of knowledge, God. We look at the example of two plus three equaling five. We see this to be clear and distinct, but it is possible that we are being deceived. He tries to dispel the doubt about propositions of mathematics by claiming that God exists and would not allow such a deception. He makes an argument for God's existence. Premise one states that we have an idea of God. Premise two states that the only way to have an idea of God is if God exists. Therefore, the conclusion is that God exists. Us having an idea of God means us having an understanding of the infinite. We can't understand the infinite through the finite, but only through the infinite, thus God must also be the cause of the idea of God. We as finite substances cannot cause the existence of an infinite substance. The idea is also an objective reality, thus it can be held as true. God is not deceiving us and now we have added the final building block to our house of knowledge.
In The Republic, Plato has his own epistemology. His is more along the lines of idealism. The ascent to knowledge is not based upon understanding an object, but understanding the idea of that object. The highest idea or form is the idea of the Good itself. Socrates is the main character of this section of The Republic. He engages in a conversation with Glaucon about knowledge. Socrates gives two images of the ascent from chaotic opinion to orderly knowledge, the image of the divided line and of the Cave. Knowledge is what is certain and true and opinion is what is fallible. This is where we may see a connection between Plato and Descartes. They both agree that knowledge must be certain and all other things false.
Plato held that all knowledge can be derived from a single set of principles. Knowledge rests on the Good as its foundation, unlike Descartes, where one's self is the foundation. Plato compares the power of the Good to the power of the sun. The sun illuminates things and makes them visible to the eye. The absolute good illuminates things of the mind and makes them intelligible. According to Plato, the idea of the Good is too much for humans to understand, but can be thought of as the idea of absolute order. The sun is the cause of generation, nourishment, growth, and visibility. The Good is the cause of essences, structures, forms, and knowledge. This is somewhat similar to Descartes because God is the cause of the idea of Himself, thus the cause of everything else also.
There are four levels of knowledge. First, there are two ruling powers though. The good is set over the intellectual world and the sun over the visible world. We start with two lines, one for knowledge and one for opinion. Now we cut them once more and now there are four sections, two belonging to the intelligible world and two belonging to the visible world, two belonging to knowledge and two belonging to opinion. The first section is that of images such as shadows and reflections. The second deals with us seeing actual things, sense-perception. Unlike Descartes, we will not discard this, but use it to build on our knowledge. Descartes believes sense-perception to be false, but Plato uses it as a stepping stone towards knowledge. Now we have the two subdivisions of the intellectual. The third section is where the soul has understanding through its assumptions based on images. The fourth section is where the soul moves past the use of any images and strictly reasons things out. One does not use objects, but ideas to reason.
Next is the Allegory of the Cave. Plato's allegory is a copy of the reality of the divided line. Plato realizes people can think and speak without being aware of the Forms. Plato treats these people as prisoners chained in a cave, unable to turn their heads. All they are able to see is the wall of the cave and a fire burns behind them. There is a place to walk between the prisoners and the fire. There are others in that place that hold up objects to cast shadows on the wall of the cave. The prisoners are unable to see these objects behind them. They see and hear only the shadows and echoes cast by these objects. Prisoners like these would mistake appearance for reality. They would think the shadows are real, but would be unaware of the causes. Plato points out that they would refer to the shadow rather than the real object. The only way for the prisoner to see what he is talking about is to turn his head around. We actually name things we can not see, but things that we can only grasp in the mind. When the prisoners are released, they can see the real objects and realize their error. The way we can see the causes of our shadows is by grasping the Forms with our minds. The prisoners now ascend upwards out of the cave( into the intellectual world). When they first leave the cave, their eyes feel pain the same way the jury that convicted Socrates felt pain. They were not used to the light just like the jury was not used to Socrates' manner of speaking. The prisoners would, at first, react violently as the jury did and try to descend back into the cave. This is similar to when the jury sentenced Socrates to death. But the prisoners must go on. Once they adjust, they are able to see the objects and what they must possess in itself. This takes us back to Descartes again. Descartes also believed we must look for an object's uniqueness without relying on sense-perception. The light shows them what the external conditions must be and then they finally see the sun, the source of the external condition.
Plato and Descartes have their own epistemologies. Plato's is that of Idealism and Descartes' is Foundationalism. They differ somewhat while they also share similarities. Plato says what we see are shadows, not the real objects. A philosopher is one who strives to see the object and what makes the object unique. Finally, the philosopher will be able to see the idea of the object. Descartes also aims to find the uniqueness of an object and the idea of it through reason, but his approach differs. He casts doubt on what he feels isn't certain and starts to rebuild his house of knowledge on what is, himself being the foundation. Plato is not necessarily looking to cast doubts on one's beliefs, but is trying to expand one's knowledge of it. Their ends are the same, try to reach the Good or God, but their means are different.