It is assumed in this article that the concept of Fenggu is abstract but not concrete, illegible but not legible, extentive but not intentive, unifiable but not antinomic.
He asserted, also, that his power to follow a long and purely abstract train of thought was very limited, for which reason he felt certain that he never could have succeeded with mathematics.
There are also detailed pictures of wild hoofed animals. Art and therefore the ability to think in abstract concepts is what distinguish our species from other animals.