Humans are animals but—essentially—they are the only rational animals. When a human sees an object they can create the idea of what makes that object unique (a tree). This is called abstraction. Animals merely see the object as a single thing (the tree). Because we can separate the idea of a thing (its concept) from the thing itself, we can combine it in our mind with other things to make new things that don’t exist in the physical world (a tree that talks, for example—combining “tree” and “human”).