It is dark but can illumine

The Way is infinitely high, unfathomably deep. Enclosing heaven and earth, receiving from the formless, it produces a stream running deep and wide without overflowing. Opaque, it uses gradual clarification by stillness. When it is applied, it is infinite and has no day or night. It is restrained but can expand, it is dark but can illumine; it is flexible but can be firm. It absorbs the negative and emits the positive, thus displaying the lights of the sun, moon and stars.

~ from WEN-TZU by Lao-Tzu