Taiji Classics:

Taiji Quan Treatise:
T'ai Chi Ch'uan Lun (太極拳論)
Wang Zhongyu, Salt Shop Manuals, Ming Dynasty

Tai Chi is born of Wu Chi, the mother of yin and yang.
In motion they separate; in stillness they integrate.
There is no excess and no insufficiency.
When the opponent stretches out, you bend,
when he contracts, you expand.

Overcoming the unyielding by yielding is called "withdrawing".
Moving with the opponent and causing his position to become ineffective, is called "adhering".

Respond quickly to quick movements, respond slowly to slow movements.
While variations are numerous, the principle remains constant.
Through mastery of the postures, you will gradually awaken the awareness of jing.
From awareness of jing you will reach a state of shen ming (intuitive illumination).
But without a long period of effort, you will be unable to have thorough understanding.

Retain a light and sensitive energy on top of the head; sink the chi into the dantien.

There should be no leaning, no inclining.
Suddenly hidden and suddenly appearing.
If the left is weighted, the right becomes empty (insubstantial).
If the right is weighted, the left becomes empty (insubstantial).
Looking upwards, it seems to become higher and higher;
looking downwards, it seems to become deeper and deeper.
When advancing, it seems to become ever farther away;
when withdrawing, it seems to become closer.

Your body should be so sensitive  that a feather cannot be added without being felt,
nor can a fly land without altering your balance.
The opponent does not know your intention, but you can predict his.
Mastering this, you will become a matchless hero.
At this point you attain the highest skill.
There are numerous other styles of boxing.
Although there are distinctions in the postures,
they do not go beyond strong overwhelming the weak and speed conquering slowness;
those with strength attacking those without strength;
those with speed overcoming the slow.

These are all just the natural abilities, and do not relate to the strengths acquired through practice and study. In examining the statement of "four ounces removing one thousand carries", it is evident that this is not a matter of superior strength.
If you see an aged man withstanding multiple opponents, what has this to do with speed?
Stand like a balanced scale, active like the wheel of a cart.

Sinking the weight to one leg, you can move at will.
By distributing your weight on both feet,
you become double-weighted (shuang zhong) and stagnant.

When we see those who after many years of training cannot employ a neutralization and are generally subdued by the opponent,
This is because they have not yet understood the fault of
double-weighting.
In wanting to avoid this fault you must know yin and yang.

To adhere is to receive; to receive is to adhere.
Yin is not separate from yang; yang is not separate from yin.
The mutual coordination of yin and yang is precisely what leads to "interpreting energy” (dong jin)
After you acquire "interpreting energy", the more you practice, themore skill you will obtain.
Silently memorize (mo shi) and ponder (chuai mo),
 you will gradually you will attain what you wish from your heart and mind (cong xin suo yu.)

The fundamental here is to yield to the initiative of the other.
Many mistakenly forsake the near in pursuit of what is distant.
This is called, "the slightest divergence leads you far astray".
Students must thoroughly distinguish between these aspects.

Every word of this treatise is important.
There is not one extra word or reference.
Without natural intelligence you cannot apprehend these words.
The early masters were unwilling to propagate false teachings and did
not trust just anyone. They were apprehensive about transmitting their kung-fu skills to others without good reason.