There’s only one chapter in Tao Te Ching that mentions Yin and Yang – if you are talking strictly about the use of the two words. They can be found in chapter 42, where Lao Tzu says:
“The Tao gave birth to One.
The One gave birth to Two.
The Two gave birth to Three.
The Three gave birth to all of creation.
All things carry Yin
yet embrace Yang.
They blend their life breaths
in order to produce harmony.”
If you’re talking about the concept of yin yang, nevertheless, then it permeates the whole book. In fact, you may describe Tao Te Ching as a book on yin yang.
“All things carry Yin yet embrace Yang,” says Lao Tzu. The forces of yin and yang are found everywhere and in everything. If you want to leverage on the power of nature, you would have to understand the interplay of the two forces.
In Tao Te Ching, Lao Tzu uses different descriptions for the forces of yin and yang, among them are being and non-being, doing and non-doing, soft and hard, yielding and rigid and many more. Although the descriptions can be different and may serve different purposes, you must not be confused. Look through the substance to grasp the essence!
“The Tao that can be described is not the eternal Tao. The name that can be spoken is not the eternal Name”, says Lao Tzu. This applies to the descriptions of yin yang as well.