Ying and Yang  The Tao gives birth to one.   
                              One gives birth to two.
                              Two gives birth to three.
                              And three gives birth to all things

The "One" is  the primal Tao, Allah, God, Brahman, Krishna... or physic's singularity.
The "One" divides itself into two, mitosis, creating Yin and Yang, the "Two".
The union of Yin and Yang make "Three", because they are the "One", the Tao.
This gives birth to all things.

In a relationship, such as a marriage there isn't two, but three.
The singular woman.
The singular man.
(or same sex marriages)
The spirit of the relationship.
The relationship gives birth to all things.
This would also be true in a friendship.

The concept of Yin and Yang  and of the Tao are exciting and revealing.
You can explore further at

Also I found
"God as Nature Sees God, A Christian Reading of the Tao Te Ching"
by The Reverend John R. Mabry MA to be a wonderful book on the subject.

"Thirty spokes join together at one hub
But it is the hole in the center that makes it operable.
Clay is molded into a pot,
But it is the emptiness inside that makes it useful.
Doors and windows are cut to make a room,
It is the empty spaces that we use."

"Existence and non-existence produce one another.", Lao Tzu
" Existence is what we have,...but non-existence is what we use."

"Spirit" in Taoism is associated with " non-existence " because there is no physical manifestation.
"God is a being beyond being and a nothingness beyond being.", Meister Eckhart.
Non-being is necessary for physical realities to exist and vice versa.

Do we exist (physically) because our spirit is our "non-existent"  yin? 
The two make the one? 
Then there are three?
This gives birth to all things?