According to Plato, behind every object and concept in the visable world, there is an unseen reality. This is a 'Form'. For example, there is a form of a tree (object) and a form of beauty (concept). The forms are looked at as ideal 'blueprints' for the earthly examples of beauty and trees. The earthly forms (trees, beauty etc) are known as Particulars. Forms exist seperatly from their particulars, almost like a different world. For example, the form of beauty exists seperatlely from our ideas about beauty and from beautiful individuals. The forms are a source of all knowledge. They are more real than their particulars, the particulars are only very pale reflections of the Forms. For example, the beauty of a painting is illusory and only a poor approximation of the form of beauty. Forms are not dependent on physical matter, they must be consistent, eternal and unchanging. They therefore cannot be detected by the senses. The particulars depend on physical matter, are changeable and imperfect. The only reason we can recognise and classify things is because of the resemblance of the particulars to the Forms, no matter how weak the resemblance is. For example, all particulars of cat have the same thing in common, although they are different sizes and colours etc, they all share something of the Form of the cat, this is how we recognise it as a cat. This is also true for equality, we recognise things as equal because we have some awareness from the Form of Equality. We cannot be aware of this from our senses because the Forms are beyond them. We have an immortal soul that had access to the Forms before it was implanted in the body. We therefore have an innate knowledge of them that can be developed through rational thought. All forms are connected to eachother in a fixed order of importance. The most important is the Form of the Good which is central to the existence of the whole universe. It gives rise to all knowledge, enabling us to recognise the other forms.