Good and Evil are they Inseperable?

First of all this will be a poem but I would like to thank one of my friends, Samia for giving me inspiration to write this.
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Light and Darkness
Good and Evil
Every light casts a shadow
For every Good deed there is an Evil one
With out Darkness would we know what Light is?
Without Evil would we know what Good is?

We need the evil to show us the good.
Just as we need to know what light is
To know what darkness truly is

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That is what I have for now. Tonight my writing just isn't flowing like usual. This is another one I'll have to revise later and hopefully add to it.