On the grand scale, the interlocking black and white shapes within the circumference of the circle are representative of the cyclical nature of the natural world. Day becomes night, summer becomes autumn, hot becomes cold … and life becomes death. The day is represented by the white section and night by the black. The dot (or 'seed') of black in the white and the seed of white in the black implies that 'nothing is all black and nothing is all white' … and therefore it follows that there is nothing that is 'all good' and there is nothing that is 'all bad', 'all right' or 'all wrong' … … … and so on. The white YANG section represents the aggressive, the quick, the loud and bright - with the thinnest being just 'dim'; somewhere between 'cool' and 'cold'; and the thickest being dazzling or 'white-hot'. Thus, the minimum Yang i.e. the whisper and feint glimmer portion of the Yang overlaps the maximum Yin.

To properly or fully benefit from Tai Chi it is important that we understand the breathing technique involved - and coordinate our movements with these breaths. The breathing technique intrinsic to this is called "Diaphragmatic Breathing". This is sometimes more popularly called "Circular Breathing" because of certain visualizations that I describe later, however the latter term actually refers to a technique used by players of some wind instruments (such as the Australian didgeridoo) to produce a continuous tone without interruption. The "Circle Breathing" in Tai Chi is more ... 'in the mind' and a thing of mental discipline and focus as opposed to a thing that requires any special or exceptional physical ability.

The graceful movements of Tai Chi Forms may, with little alteration can function as a martial art fighting form of Tai Chi Chuan - and in this respect - all of the postures within the Form may be categorised as either 'offensive' or 'defensive'. Accordingly, all defensive postures (or 'moves') are performed on an in breath - and all offensive postures/moves are made on an out breath. Furthermore, a defensive move is classified as a "Yin" and an offensive as "Yang".
So the theory is: Defense on the Yin or In breath and offense on the Out or Yang breath.

The natural, instinctive way to add power to any intended 'out' or away or push movement is to first set yourself, breathe in and then … puuuussshhhhhh on the out breath. We do this all of the time to a greater or lesser degree in our everyday activities, from opening a stuck door through to pushing your broken-down car. When we are not doing this, we are, to a greater or lesser degree, doing the opposite! For instance, you see a bird flying towards you and you fear that it may be a little low and it will have your hat off. What do you do? You breathe in and turn side-on by bending and sinking at the knees a little. Doing the dishes, you drop a cup. What do you do when it hits the floor and shatters? You take a sharp in breath as you jump back a little and raise your hands towards your face, subconsciously protecting your eyes from shards. Sometimes, because of the same primitive instinct, we might even shut our eyes or squeeze our lips together. Our ancestors did the same when snakes and such like creatures spat who knows what at them!

http://en.wikipedia.org/wiki/Diaphragmatic_breathing
"Diaphragmatic, abdominal, belly, seesaw, deep or costal breathing is the act of breathing deep into your lungs by flexing your diaphragm rather than breathing shallowly by flexing your rib cage. This deep breathing is marked by expansion of the stomach (abdomen) rather than the chest.

It is generally considered a healthier and fuller way to ingest oxygen, and is often used as a therapy for hyperventilation and anxiety disorders.

Note that some yoga and meditation traditions draw a clear distinction between diaphragmatic breathing and abdominal breathing or belly breathing. The more specific technique of diaphragmatic breathing is said to be more beneficial.

Though the diaphragm is the primary breathing muscle, it is believed that many people have little sensory awareness of their diaphragm and almost no idea of how to engage it more fully or even of how it works. There are some breath therapists and breathing teachers who believe that because of the increasing stress of modern life and the resulting over-stimulation of the sympathetic nervous system, as well as of the idealised hard, flat belly, that many people carry excessive tension in the belly, chest, and back, and this tension makes it difficult for the diaphragm to move freely through its full range of motion". more ...

http://en.wikipedia.org/wiki/Diaphragm_(anatomy)

In the anatomy of mammals, the thoracic diaphragm is a sheet of muscle extending across the bottom of the rib cage. more ...

(1) Esophagus
(2) Thoracic diaphragm
(3) Stomach
(4) Liver
(5) Gallbladder
(6) Duodenum
(7) Pancreas
(8) Spleen

http://en.wikipedia.org/wiki/Tai_chi_chuan
As the name "tai chi chuan" is held to be derived from the Taiji symbol (Taijitu or T'ai chi t'u), commonly known in the West as the "yin-yang" diagram, tai chi chuan is therefore said in literature preserved in its oldest schools to be a study of yin (receptive) and yang (active) principles, using terminology found in the Chinese classics, especially the Book of Changes and the Tao Te Ching. The core training involves two primary features: the first being the solo form (ch'üan or quán), a slow sequence of movements which emphasize a straight spine, abdominal breathing and a natural range of motion; the second being different styles of pushing hands (tui shou,) for training movement principles of the form in a more practical way. more ...

http://en.wikipedia.org/wiki/Pushing_hands
Pushing hands is said to be the gateway for students to understand experientially the martial aspects of the Internal martial arts; leverage, reflex, sensitivity, timing, coordination and positioning. Pushing hands works to undo a person's natural instinct to resist force with force, teaching the body to yield to force and redirect it.

Health oriented tai chi schools may teach push hands to complement the physical conditioning available from performing solo form routines. Push hands allows students to learn how to respond to external stimuli using techniques from their forms practice. Among other things, training with a partner allows a student to develop ting jing (listening power), the sensitivity to feel the direction and strength of a partner's intention. more ...

http://en.wikipedia.org/wiki/Kung_fu
Kung fu or gongfu or gung fu is a well-known Chinese term often used by speakers of the English language to refer to Chinese martial arts. Its original meaning is somewhat different, referring to one's expertise in any skill, not necessarily martial.

The term "kung fu" was not popular until the 20th century, thus the word would be seldom found in any ancient texts. The term was first known to have been reported in the 18th century by a Westerner, French Jesuit missionary Jean Joseph Marie Amiot, and was known little in the mainstream English language until approximately the late 1960s when it became popular because of the Hong Kong films, especially those by Bruce Lee, and later "Kung Fu" - the television series. Before that it was referred to primarily as "Chinese boxing".

Translation and Interpretation
It is hard to translate "kung fu" into English as we have no equivalent. In short it means "achievement through great effort" or simply virtue. It combines (kung) [sometimes gong] meaning achievement or merit, and (fu) which translates into man. In Mandarin, when two "first tone" words such as gong and fu are combined, the second word often takes a neutral tone, in this case forming gongfu.

Originally, to practice kung fu did not just mean to practice Chinese martial arts. Instead, it referred to the process of one's training - the strengthening of the body and the mind, the learning and the perfection of one's skills - rather than to what was being trained. It refers to excellence achieved through long practice in any endeavour. You can say that a person's kung fu is good in cooking, or has kung fu calligraphy. Saying that a person possesses kung fu in an area implies skill in that area, which they have worked hard to develop. Someone with "bad kung fu" simply has not put enough time and effort into training, or seems to lack the motivation to do so.

For a process to be truly kung fu; motivation, self-discipline and time must be present.