Plato was a rationalist philosopher. He makes the assumption that truth and knowledge only apply to what truly exists. So he resricts the term 'knowledge' to simply our awareness of the forms. We do not have knowledge of things in our world as they do not exist, they only exist in the realm of the forms.
The perfect idea of what a thing is. The do not exist in the physical world, but everything in the world is made in the likeness of its form. There are also forms of non-physical things like beauty and honesty.The forms are perfect, non-physical and eternal.
The Realm of The Forms:
It is eternal, unchanging and perfect, unlike the the physical world which is impermanent, changeable and imperfect. Everything in the physical world is made in the likeness of the Forms.
The Form of The Good:
There are so many form sthat there must be a 'form of forms'. Plato calls this supreme Form the 'Form of the Good'. It is the most important form. All perfection comes from it. It makes objects able to be known and is the source of their existence.
Explainations and Allegorys:
If something is true in the realm of appearences, then it is fully true in the realm of the forms. In the realm of objects we need eyes to see them. In the realm of the Forms we need the force of intellect to appreciate the Forms. We also need a 'sun equivilant' which is the 'Form of the good'.
The simile of the divided line explains that we can only have opinions based on belief and imaginationin our realm, which are based on percieving physical objects and images of physical objects. Knowledge is what we have in the realm of forms though reason and understanding of the Forms and mathematical objects through the Form of the Good.
The simile of the…