The Yin and the Yang of it

[Kaiserin]

Yin/Yang is an eastern principle which posits that:

- Everything good has within itself a grain of evil; likewise, everything evil has a grain of good.
- For every amount of good, there is an equal amount of evil.
- Good and evil are coexistent, and even codependent (one cannot exist without the other).

I was thinking... how true or how applicable can this be in M-E?

For example:
- Eru-Iluvatar: He is considered entirely good, yet he permits evil (?). Could he perhaps have a margin of error, or probably a need for evil to make himself appear good against?
- Orcs: They are considered definitely, undoubtedly evil. But perhaps they have some capacity to do good?
- The Valar: Eru intended them to be wholly good, but we all know what happened to Melkor.

Can one be considered evil if he possesses in fact that grain of good within himself(think of Smeagol / Gollum...)?

Why is a "good" man still considered "good" even if he has a little grain of evil within him?

Would there be such a thing as "good" and "evil", if both of these are within the permissible will of Eru in the macrocosmic level of things?

Ideas, ideas, ideas...