Thought.

Inside a sealed box, it would be dark.
If you shone a light on the box, something full of darkness would cast a shadow.
If you opened the lid on the box, and shone a light on it,
something full of light would cast a shadow.
There is only one type of shadow. Only one definition.
Shadows are not darkness.
Shadows are not light.
Shadows are surrounded by light.
But darkness isn't necessarily surrounded by anything.
Shadows are not darkness.
Darkness can be used to define light.
Light can be used to define darkness.
But only light can define a shadow.
shadows show the beauty of light. Darkness just sucks.