Plato’s Theory of Forms claims that the world which we perceive with our senses is merely a representation of the real world which is only intelligible through our minds. The intelligible world contains the Forms which are changeless, absolute and abstract. They exist in permanent relation to the visible world, making the visible world possible. The realm of the Forms is a realm of ‘universals’ and the material world is full of ‘particulars’, inferior copies which are in a constant state of change and decay.
Plato supposes that all things have a true Form. One way he supports this theory is by the Argument of Human Perception in which he claims that, because we are able to recognize consistent qualities through varied circumstances, we must draw from a master template of sorts. For instance, we recognize that a red apple, a green apple, a yellow apple, and a rotten apple are all apples. Plato maintains that is because the apples are ‘participating’ in the Form of ‘appleness’. He goes on to suggest that we recognize this ‘appleness’ because we each possess an eternal, unchangeable soul which was once connected to the real world of the Forms and, for that reason, when we are born, we are able to recognize them.
Along with developing a theory that would explain how we share a common perception of the world around us, Plato was interested in answering more complex questions which were inspired by his ‘teacher’, Socrates. Questions such as: Can we truly know the meaning of justice or virtue or goodness?
With his theory in which all things have a true, universal Form – perfect, unchanging, and extending beyond space and time – Plato’s answer to that question is – yes, we can know the true meaning of Justice and Virtue and Good.