Since the world points up beauty as such
There is ugliness too.
If goodness is taken as goodness
Wickedness enters as well.

For is and is-not come together;
Hard and easy are complementary;
Long and short are relative;
High and low are comparative;
Pitch and sound make harmony;
Before and after are a sequence. – Lao-Tzu

(WOL:  Lao-Tzu, The Way of Life (Tao Te Ching). Trans. R.B. Blakney. New York and Scarborough:
New American Library, 1955, 2, 54.)