According to Plato, because we understand the concept of the Ideal Form, without experiencing them, our souls must have known the Forms before we were even born. This leads him to the belief that people must therefore have immortal souls.
Plato believed that when we use words such as “frog” to describe a particular animal we see, we are not just classifying it. We are referring to some particular quality that it shares with all other animals that are also described as “frog”. They all share something of the Form of the Frog. Plato developed this idea further by claiming that, in the world of the Forms, there is an ideal Frog, created by God. The frogs we see as we go about our daily lives are inferior, superficial versions of the Ideal Frog. They are constantly changing, they are born, and they die; whereas the Ideal Frog is eternal and unchanging, and is the subject of knowledge not opinion.
Another method used to help people understand the Theory of Forms, is to consider it in terms of mathematics. For example, a circle is a two dimensional shape with a series of points arranged around a centre. This is not a matter of opinion, but something we know. No one has actually ever seen a perfect circle. A perfect circle could not be seen; the infinite points which make up its circumference do not take up any space, they exist
in logic rather than in a physical form. As soon as someone tries to draw it, even if becomes imperfect. But although the Ideal Form of a circle has never been seen, and never could be seen, people do know what a circle is they can define it while at the same time accepting that it cannot be translated into the material world without losing its perfection.
For Plato, therefore, the Form of a Circle exists, but not in the physical world of space and time. It exists as a changeless object in the world of Forms or Ideas which can be known only by reason. Forms have greater reality than objects in the physical world both because of their perfection and unchangingness, and because they are models. As Ideals, they give ordinary physical objects resemble the Forms; just as the shadows, in the Analogy of the Cave, only had any kind of existence because of their resemblance to their corresponding physical objects. Circularity, squareness, and triangularity are all examples of what Plato meant by the Forms. An object existing in the physical world may be called a circle or a square or a triangle only to the extent that it resembles the Form of circularity, squareness or triangularity.
Plato believed that the Forms were connected and arranged in a kind of hierarchy. The most important Form is the Form of the Good, which is the ultimate principle. Like the Sun in the Analogy of the Cave, the Good illuminates the other Forms. We can see that justice, for example is an example of goodness. We know that we have never seen or experienced real goodness in its true Form, but we have seen some good examples which approximate goodness, and we recognise them as good when we see them because of the way in which they correspond to our innate notion of the Form of the Good. By Plato’s logic, the real knowledge becomes, in the end, a knowledge of goodness; and this is why philosophers are in the best position to rule.
Plato developed his theory of Forms to the point where he divided the existence of the world into two realms. There is the world of sense experience (the empirical world), where nothing ever stays the same but is always in the process of change. Experience of it gives rise to opinions. There is also a world which is outside space and time, which is not perceived through the senses, and in which everything is permanent and perfect or Ideal- the realm of the Forms. The empirical world shows only shadows and poor copies of these Forms, and so is less real than the world of the Forms themselves, because the Forms are eternal and unchanging, the proper objects of knowledge.
