Plato’s Theory of Ideas AKA Theory of Forms

Prequisite:
Overview of Plato’s Philosophy

Theory of Ideas

By Ideas, Plato means the essence of a particular thing, that is universal for all types of that particular thing.

Ideas are things in themselves, something that exists by the virtue of its own existence. It is independent and does not depend on anything else for its existence. For example, an Idea of a Horse exists beyond space and time, they are non-spatial and non-temporal. However, the existence of a Horse on earth depends on various other factors, such as matter, air, food etc and therefore, they are particulars/form of the Idea or essence or something that is universal to “Horse-ness”

One Idea of Horse-ness ; Many Forms

Theory of Forms

By forms, Plato means the same thing as that of ideas. The shape, form and existence of a particular thing in the World of the Senses depends on Forms or Ideas of the World of Ideas or World of Forms.

How Plato consolidates his above theories …

1. An Argument from Science
   By Science, Plato means academic disciplines that are based on objectivity i.e objects of knowledge which are true in all instances and unchanging. To explain, he takes the discipline of mathematics wherein the definition of a straight line is that of the shortest distance between two points, which has position and no magnitude. In the real world, there is nothing in space and time which has position but no magnitude. Yet the concept exists — which is unambiguous and absolute taken from reason — and is applied in the World of Senses.
2. The Argument of one over many
   As in the case of the above picture of horses, the same can be applied to many particulars in the World of the Senses. For example, one Idea of a Tree has particular existence in the form of many. Meaning, Idea is one, particulars are many
3. The Argument of things which are no more
   Particular things are born, and they die. Yet, the idea or essence of that thing is everlasting i.e eternal, immutable, non-temporal. For example, Dinosaurs.
4. Argument from Relation
   For example, Tony, Jack and Simon can all be related under one umbrella of Men, under the Idea of ‘Man-ness’ — though each one of them is different from the other
5. Argument from Relation that implies the Third Man Fallacy
   Whenever Particulars are similar but different, there must be something common between the two that makes it similar. For example, if A is like B, and B is like A then there exists something that is universal between them. Likewise, between a particular man and a universal man there must exist something between the two.

Next:
World of Ideas and World of Senses