Our son (8 years old) was stating yesterday that all things have opposites. He

Our son (8 years old) was stating yesterday that all things have opposites. He was discussing the matter with our daughter (10) and she argued that it cannot be so. The examples our son provided were of the kind light vs dark, day vs night, cold vs hot. I tried to explain the oriental idea of the TAO, the whole being composed of Yin and Yang, both opposites but complementary and each with a touch of the other. Another example I tried to make was the definition of a vase, or a bowl or any vessel that is defined by its content. An empty vase not being anything without just "nothing" inside. The question our daughter raised was then: What is then the opposite of a lion? Or a tree, or a rock?... I had a hard time trying to get a good answer for that one and settled for a non-lion, no-tree or no-rock (thinking of the vase allegory above). My question to you is then, what would your answers be? Is there really a duality in all things and if so, how does it apply to the lion case? Thank you.

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