Another discussion of "Mnemonic Principles of Taiji", this one with additional comments, appears in the essay "What Is T'ai Chi?":

The Five Tai Chi Principles

Relax ~ Be Soft

Relaxation is the first and foremost principle. Not at all weak or limp nor tight and stiff, this is an alert, vibrant condition that promotes fluid gracefulness while enhancing sensitivity, a prime requirement in our world of constant change. T'ai Chi coaxes the body into loosening and opening so that internal energy may flow freely. Blood circulation is enhanced as the capillaries open, for example. Tension is a blockage resulting from stress and/or trauma. Regular practice with mental concentration provides early recognition and amelioration of physical and mental tension.

Keep the Body Upright ~ The Straight Spine ~ Do Not Lean

Verticality of the spine is another important principle. Leaning even slightly in any direction means tensing the body in a losing battle with gravity. The top of the head is kept horizontal and the spine upright and open so the muscles along the spine may relax. The spine is a major energy path that deserves close attention. After the common cold, back pain is the most frequent ailment reported and it is often caused by tension due to poor posture. Mother was on to something when she said, "Sit up straight!"

Turn the Waist ~ Do Not Twist the Spine

The center leads the movement of the energy and the body. The waist area just below the navel is the central axis or hub of the body and the limbs may be thought of as spokes. Paying attention to the center on the physical level gradually leads to the meditative aspect of T'ai Chi as well. Breathing is deepened and enhanced by concentrating on the center.

Yin and Yang ~ Separate Weight ~ Empty and Full

Differentiate yin and yang and perceive substantial and insubstantial. Initially, this means to separate the weight completely in the legs. T'ai Chi is called one-legged boxing because of this emphasis on standing on one leg at a time. Obviously, this builds strength and balance. Gradually, one becomes more sensitive to other differentiations as well.

The Beautiful Lady's Hand

Beautiful Lady's Hand refers to a straight and relaxed wrist. During the form, the wrist is almost always straight in order to enhance the flow of energy. If a soda straw, for example, is bent or twisted, the flow through it is reduced. Precision of wrist position also requires concentration and practice to attain and thus builds awareness.

...and then a final comment:

Anyone Can Do It

If one were to follow the five principles only, they'd be doing the Form 80% correct. These principles are from the classics. Don't think "I can't do it." This is not true. Anyone can do four of the five principles, all except Relax. If you could Relax, then you would not need the other principles.

(cf. "Principles of the Cheng Man-Ch'ing Simplified Yang Style Tai Chi Chuan" Mnemonic Principles of Taiji (2014-03-24), ...) - ^z - 2017-09-15