One, Two, Three
 

TTC Ch. 42 (Feng, English)

The Tao begot one.
One begot two.
Two begot three.
And three begot the ten thousand things.

This paragraph confused me for many years. Only when I began to study the I Ching did this fall into place since the above is referring to change.

Tao can be thought of as absolute potential. Within potential all things are possible but nothing is actual.

The expression "Tao begot one" means that from this potential an actuality was formed. A "thing", so to speak. But this "thing" was not complete in the real sense. It was somewhat abstract, like a thought-form. This can be expressed as a single, unbroken line:

-----

The expression "One begot two" means that this actuality, this thought-form, produced a second, different thought-form. But, like the first it was still abstract. The second form can be represented by a broken line:

-- --

The expression "Two begot three" introduces the concept of change. Change is how one thing transforms into another. We can express this concept with two lines, one above the other. For example:

-----
-----

or

-- --
-----

Here we have the idea of a solid, firm item remaining solid and firm or a solid, firm item changing (yielding).

The concept of change is also semi-abstract, but it introduces the missing and needed element to manifest potential into reality, which brings us to the last line: And three begot the ten thousand things.

Ten thousand things is shorthand for "everything." This says that change begot all things, and is the complete expression of Tao.

Hope this helps.

The Tao gave birth to the Universe (One) which gives rise to Yin and Yang (Two), whose interaction creates Energy/Qi (Three) from which comes Everything (Ten Thousand Things).

TTC=Tao Te Ching for those people new to this.
A book by Lao Tzu

This is also a good way to express it. Often Yin and Yang are noted as broken (-- --) or solid (-----) lines, and Qi is energy in motion, which is a form of change, so I think you and I are in agreement.

Yes Yin is broken and Yang solid.

if things exist, that is one. If those things start wondering about non-existance, that is two. The gate between those two things make three. And it progresses from there...