Realistically speaking, all motion must travel on either a line, a circle, or some combination of these two patterns; there are simply no other options.
But, before this discussion goes any further, a quick understanding of how motion is created in the human boy is warranted. First, all motion in the human body is initiated through joints. Joints can be thought of as intersections where the otherwise stiff parts of the bones are allowed to bend. Thought of in a slightly different manner; our body is made of bones; bones are hard and non-flexible. So, in a way to get around this design, there are places where the bones may bend. These places are called joints. There are other ways more flexible (non-skeletal) bodies, such as an octopus, maneuver and bend, but that is outside the scope of this discussion. This discussion is limited to skeletal bodies.
The interesting thing about joints is that they only work on circles. In other words, in order for a joint to bend the two stiff parts of the bones that they join, they pivot. And by definition, pivot means circle. If one were to stop at this point of the analysis, it would be reasonable to draw the conclusion that because of this presented fact, that all motion in the human body must be circular. But that deduction is only partially true.
It is true that all joints pivot and therefore work on circular motion, but the body contains a large number of joints at various points. And this is significant because if more that one of these joints is combined together, in the right way, the generated output motion can be a straight line. Working with these facts, the following truths may be synthesized:
The use of one joint in the body will always produce a circular motion.
If two or more joints are combined together properly, a linear motion can be achieved.
If two or more joints are combined together properly, a circular motion can be achieved.
With these truths all possible options for travel are satisfied. And, although this information is not necessarily needed for an overview of circles and lines as a subject, in and of itself, it is relevant because it is upon these principle foundations about the human body that further examination into motions generated by the human body may build.
Note: This information is also useful if applied to the next Appendix on pivots and levers.
Moving onto further analysis of motion, and starting with the options presented above, there are a limited number of possibilities available that may be deduced:
First, if a linear or circular path is started that path can be continued.
Second, if a linear or circular path is started, that path can be reversed.
Third, if a linear or circular path is started, that path can be deviated into a new linear or circular path.
Fourth (which is almost a corollary to #3), if a linear or circular path is started, it can be converted from one to the other (and potentially back again).
In American Kenpo, we have given these options more colloquial labels:
#1 = continue
#2 = reverse
#3 = deviate (linear) / switch or adjustment (circular)
#4 = change or convert (linear or circular) / cut (circular)
One of the major themes of Long Form Three can be succinctly described as an introductory study into motion traveling on circles and lines. It is these two route choices, and the switching between one or the other, that is introduced in a major way with Long Form Three. Long Form Three uses the above foundational information, along with other principles of motion, and presents it, almost surreptitiously, through the applications presented throughout the form.
Put another way, Long Form Three exposes and introduces the foundational principles, rules, and options related to lines and circles in a way that one who understands the motions will be able to recognize and reconstruct the intended information; but one who is unaware of this thematic analysis will not be alerted to its presence. Furthermore, this method of hiding information in plain sight was done purposefully and as part of the overall design of Long Form Three (and other forms of the system).
For more information about the rationale for making these critical pieces of information so non-obvious, refer to the Execution, Standard section of this book; as well as many other historical sections throughout this guide series as a whole.
It is almost imperative to mention at this point that Long Form Three is not designed to be totally comprehensive on this subject. As stated, it is merely an introduction. Therefore, a practitioner should rightly expect this subject to be expanded upon elsewhere. And it is.