1. The Theory of Forms or The Theory of Ideas
Plato
The Theory of Forms or
The Theory of Ideas

2. The Theory of Forms/Ideas
Fernando is a Man.
Lucca is a Man.
How can we say that Fernando is a Man and Lucca is a Man?
There must be something in common between Fernando and Lucca that enables us to say that both of them are Men.

3. The Theory of Forms/Ideas
This Argument can be applied to everything, to every name or property of things we can think of.
E.g.: we say that the sky is blue; jeans are blue, and blue is the color of the marker on the board.
But there is a Problem!
The sky is not constantly blue – in time (tomorrow it will be white), or in space (the shade of blue we see here is not the same shade of blue in Pirapora)!
The jeans’ shade of blue fades over time!
The blue line drawn on the board can be erased!

4. The Theory of Forms/Ideas
So, how can we say that they are all blue?
What makes blueness?
Is it, by any chance, the sensible property (the physical property that shows a certain kind of blueness)?
But then, since in every blue object the shade of blue is different form the others, we would have to use a single, different word to refer to every different kind of shade of blue.

5. The Theory of Forms/Ideas
The problem here is a very important one that appears all over the History of Philosophy:
the relation between unity and multiplicity
We find multiple shades of blue in multiple different objects.
However, we refer to all these different objects and different kinds of blue by a single word: Blue!

6. The Theory of Forms
Heraclitus – “We cannot step twice in the same river” – “There is nothing permanent except change”

7. The Theory of Forms
Parmenides – “Being is; non-being is not” – “Thinking and being is the same thing” – “Change is an illusion”

8. Parmenides vs Heraclitus
Arché = Being
Logic:
Principle of identity
– One thing is equal to itself
Principle of non-contradiction
– One thing cannot be and not be at the same time
Arché = Fire:
Contradiction
– Nothing simply is, everything becomes and ceases to be.
– Unity is multiplicity – one thing cannot exist without its opposite and everything brings its opposite inside itself (cold and hot, asleep and awake, day and night).
Parmenides
Heraclitus

9. Parmenides vs Heraclitus
Ontology:
– Being is and can be thought; what we can think really exists.
– Non-Being is not and cannot be thought; what we cannot think doesn’t exist.
– Being is immutable, uncreated, eternal, identical to itself.
– Movement and change are illusions.
Ontology:
– The World is in a perpetual flux of change.
– Change and movement is the ultimate reality.
– Being is ever changing.
Parmenides
Heraclitus

10. Plato’s Answer to the Debate: Heraclitus X Parmenides
What is the ultimate reality?
Does Being change perpetually or is it immutable?
Plato:
Heraclitus is right to say that everything we perceive is in a perpetual flux of change
But if we extend this conception to everything, then we could not know anything (and could not even name things, because they would constantly change)
But Parmenides is right to say that Being cannot change; because what is true cannot change, it must remain true throughout time

11. Plato’s Answer to the Debate: Heraclitus X Parmenides
Sensitivity X Intelligibility
Unity X Multiplicity
Forms/Ideas are the ultimate reality
But they are connected to Sensible things

12. The Theory of Forms/Ideas
Sensitivity X Intelligibility
Heraclitus is right when he talks about the Sensible World
things we can see, smell, listen, taste and touch are in a perpetual flux of change!
Parmenides is right when he talks about the Intelligible World
Blueness, or the idea expressed by the word ‘man’ are unchanging and immutable!

13. The Theory of Forms/Ideas
Unity X Multiplicity
The Sensible World presents to us the realm of multiplicity (many blue things; many men)
Sensible things are multiple, changeable (Heraclitus)
The Intelligible World contains only one Form/Idea of ‘Blue’, one Form/Idea of ‘Man’
Forms/Ideas are unique, unchangeable, immutable, eternal, perfect, intelligible (Parmenides)

14. The Theory of Forms/Ideas
Plato’s Ontology
True Reality does not change and it is purely intelligible, only the sensible reality comports change and movement – real things
(Parmenides is right and Heraclitus is wrong)
The Sensible World is also Real, but less real than the Intelligible World; so, if the Sensible World is Real, but not as real as the ideal one, than Non-Being is – shadows
(Heraclitus is right and Parmenides is wrong)

15. The Theory of Forms/Ideas
Relation between Forms/Ideas
and Sensible Things
Sensible things are connected to Forms or Ideas; nevertheless, they are different: the sensible thing is different from the Form/Idea by which we name the sensible thing
We can identify the blueness in the sky and on a pair of jeans because both sensible, particular, multiple shades of blue participate into the intelligible, universal, unique Form/Idea of Blue

16. The Theory of Forms/Ideas
Forms or Ideas are not sensible – this means that: they are not contained in time or in space, do not change, remain equal and identical to themselves

17. The Theory of Forms/Ideas
Problem! The Third Man Argument!
Let’s say: ‘Ricardo is a Man’
Ricardo is a Man because he (particular, individual, sensible being) participates into the Form/Idea of Man (universal, unique, intelligible Form/Idea)
But there are a plurality of Men that constitutes the group of every individual we can say is a Man
Then, the Form/Idea of Man can be another individual inside a larger group Men – and therefore we must assume there is another Form/Idea of Man that comprises the group of Men and the first Form/Idea of Man
And this second Form/Idea of Man, on its turn, can also be added into the group ‘every individual Man + first Form/Idea of Man’, ad infinitum

18. The Theory of Forms/Ideas
Next Class
Plato’s solution for the Third Man Argument
The Allegory of the Cave
Revision

19. Forms or Ideas are the translations in English to the term ειδος (eidos)