Since the dawn of philosophical thought there has been a desire to find truth. Now exactly what truth is depends upon whom you ask. Philosophers have been searching for truth in various forms for at least as far back as Aristotle in the first century B.C. all the way up to Carl Hempel in the 20th century A.D. To Aristotle and Plato truth was reality; To Descartes truth was found in God; To Hempel truth was found in explanation. None of these are accurate and yet all of them point toward the same truth. Reality, as defined by Plato and Aristotle, God, as proved be Descartes and ideal explanation as modeled by Hempel, all allude to the same thing. They point out that mankind is a finite being and that truth is only attainable in infinite understanding, an impossibility of man at our current stage of development.
Two of the earliest known men to approach the study of reality, or metaphysics were Plato and his student/rival Aristotle. These two inquisitors of reality looked at it from opposite schools of thought. Plato sought after answers by looking at the world with an outside/in point of view. Meaning he used what he perceived in the world to draw conclusions. Aristotle on the other hand approached the world from an inside/out perspective. He applied his thoughts and beliefs to the world. Aristotle's beliefs lead to him seeing only one level of reality. He felt there was only one imminent world and that forms existed within particular things. Aristotle held that form had no solitary existence and existed in matter. In order to explain that form is an inherent trait of matter he quotes Antiphon and "points out that if you planted a bed and the rotting wood acquired the power of sending up a shoot, it would not be a bed that came up, but wood". (Matthews, pg. 9) To Aristotle the form of the matter was wood and form is the unchanging reality. Plato's view of metaphysics shows two realms to our reality: there is the realm of changing, sense-perceptible, becoming things and a realm of forms; eternal, fixed, and perfect. The realm of form was the source of all reality and of all true knowledge. Both Plato and Aristotle use form to describe reality, which to them is truth, as being eternal in nature. So truth is eternal, or infinite in nature, but what of Plato's other realm, the realm of perception.
Plato, in the republic, gives an in depth explanation of how he views this sense-perceptible realm. He uses his allegory of the cave. In the allegory, Plato compares people, unlearned in his theory of forms, to prisoners chained in a cave. They are unable to turn their heads. All they can see is the wall of the cave and behind them burns a fire. Between the fire and the prisoners there is a parapet, along which puppeteers can walk. The puppeteers, who are behind the prisoners, hold up puppets that cast shadows on the wall of the cave. The prisoners are unable to see these puppets, the real objects that pass behind them. What the prisoners see and hear are shadows and echoes cast by objects that they do not see. Such prisoners would mistake appearance for reality. They would think the things they see on the wall were real. They would know nothing of the real causes of the shadows. So if the prisoners were to talk to one another about a passing object and called it a doll they would think they are talking about a doll, but they are really talking about a shadow. (Plato, Book VII) Plato portrays in his allegory of the cave a dualistic view of truth. He speaks of the eternal properties of form as Aristotle does, but he also adds his insight into mankind's finitude and inability to perceive the realm of forms completely. The fact that people take as truth what they perceive will plague philosophers into the modern era.
Much later, in the 17th century A.D., in his Third Meditation Descartes proves the existence of God. He builds his entire argument upon his proof in the previous meditation that in order for him...