Agnosticism: The view that the world is indescribable, unknowable and constantly changing. Our thinking can't reflect the material world correctly. To sum up, both knowability and agnosticism are discussing whether the material world can be perceived by human beings! Thinking belongs to the category of consciousness, and existence belongs to the category of matter. "Identity" can be simply understood as "identity", that is, whether the reflection of human thinking on reality is the same as reality! The same is knowable, but the different is unknowable.