Parmenides reasoned as follows:
1. Every idea has its corresponding object in the external world.
2. Thought therefore has being for its objective content.
3. If a thought did not have a referent, it would refer to nothing, i.e. non-Being.
4. Hence all concepts must have corresponding real objects, for otherwise they could not be thought. A nonexistent Being is absurd.
5. Therefore thought and the thing thought about are one and the same thing.
6. Since Being is all that can be thought, Being is all that exists. Being cannot become non-Being, which would be a contradiction.
7. All Being is therefore one and the same substance or essence.
8. Therefore the real world is completely full of fixed, eternal, unchangeable, indivisible, homogeneous Being.
9. To say that a thing is, implies that it occupies space. But empty space cannot exist, for the same reason that non-Being cannot exist.
10. It is impossible that Being could change into something else, or move into a previously empty space, so change and motion are illusions. Hence the entire 'empirical' world of appearances is nonexistent.
These seemingly logical but strange conclusions are features of Parmenides "epistemological monism". They are in direct opposition to Heraclitus' view. Both are exaggerations that provided no adequate motivation or foundation for science.
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