Martial artists are adept and managing change because they can feel their body and control it.
The better they can feel their body and how the parts relate the more able they are to use their connection to their opponent (or partner) to sense changes as they occur. They can then respond by changing their own body to suit.
In Tai Ji, substansive is a term that refers to when someone is firm. Insubstansive is used to refer to someone who is soft. You can also use these terms to refer to the part (or parts) of your body that are firm and the part that is soft.
When someone is substansive, their whole body is unified, perhaps even stiff or stable and as a result it is easy to move or manipulate that person. When someone is soft or insubstansive (but yet substansive enough to stay upright) then they do not resist when pushed or pulled. They are hard to grab a hold of, or if held, hard to manipulate or lock down.
While martial artists might vary their body between substansive and insubstansive to win a fight, you can use these ideas to control your body based on what you are trying to do.
For example you can make a part of our body substansive so that it can act as a foundation for another part of your body. You can also make a part of yourself substansive to add weight to a pose so that you can then use that weight to help you stretch. You can make a part of yourself (or all of yourself) insubstansive or relaxed so that you can stretch or so that you can practice feeling your body (and the parts there of.)
Connection is important in the context of managing change because it is via connection that you can sense change and create it.
In general terms a connection is something that joins two parts or two pieces or two ideas and creates a relationship between them.
In some cases connection allows the flow of change between the parts that are connected. In other cases connection allows the connected parts to withstand change... and stay connected.
You can generalize and say that connection either allows change to happen or resists it.
With respect to your body you can say that connections allow you to sense your body and how the parts relate. They also allow you to create change by changing the relationships between the parts of your body. Connections also allow your body to withstand change.
The better you are at sensing and controlling the connections between the parts of your body the better able you will be at both handling change and managing it.
The same principles can be applied to relationships outside of your body.
Part of the way that you can manage change within your body is by varying the tension between the parts. You can change the tension in your body by shifting bones relative to each other and relative to gravity so that the weight of your body causes tension. You can also use your muscles to pull on the relationship between bones, again causing or changing patterns of tension within your body.
If you become aware of tension, both its lack or its presence, you can use this information to inform you of the state that your body is in. If in addition to sensing your body you sense your connection to the earth you can use that connection both to sense any changes in your relationship with the earth and also to help control it.
(See the section on balance for more information on this.)
Engaged with a partner or opponent, by sensing changes in tension you can feel what they are doing as they are doing it. You can then respond. By sensing change as it happens, and responding as it happens you can get better at managing change, whether it is an attempt at a throw, an incoming foot or fist, or an attempt to pull you off balance.
Whether engaged with ourselves or a partner, the more aware we are, the more sensitive we are, the sooner we can sense change and the sooner we can work at managing change.
When you look at something like a billiard ball, you can say that it has a well defined center because all the component parts of the billiard ball are connected and those connections are strong and firm. Thus when you hit the cue ball with your cue stick, the ball moves.
It rolls along the table and depending on how you hit it, it may spin in one direction or the other as well as roll. And then when it impacts the target ball, that ball also moves.
A water bed mattress full of water does not have a well defined center. Imagine trying to move a water bed or even trying to push it. It deforms and nothing else happens unless you push to the limits of the mattresses elasticity. Ideally at this time the mattress doesn't break, it simply shifts as you push on it.
Now, because it is deformed, you can say it has a center. You've tightened some of the connections between the parts of the water bed mattress and now you give it a center of sorts. You can push it on it and it moves. However, if you vary the way that you push on it, it can relax and become flaccid.
Something that is substantially connected, like a billiard ball, retains its shape, its rigidity, its center, no matter from what direction you push or pull on it. Something that is insubstantial does the opposite.
If you tense your whole body then all the parts of your body become substantially connected, and if you maintain your tightness (or tone) you can be easily pushed, pulled or manipulated.
Depending on the circumstances this can be good or bad.
Insubstansive is the drunk who doesn't get hurt when he or she falls down because he or she is so relaxed. Substansive is the diver who controls his or her body perfectly while turning in mid air before arrowing through the water.
In either case, knowing what you want to happen you can respond by hardening or relaxing.
You work at managing changes within your body and in the process affect changes outside of our body. You can make it easy for someone to carry you or hard, or you can change between the two.
How do you learn to control your body to the point that you can vary freely between these extremes? By maintaining or improving your body's flexibility and strength and by working on you ability to sense your body and control it.
This is how you manage change within your body and how you can use your body as a device for creating the change that you desire.
If your think of your mind and your thoughts or the ideas within it as separate entities, you can label our mental state as substansive or insubstansive.
When your mental state is substansive you can be pushed around because you are attached firmly to a particular idea.
When your mental state is insubstansive, what is happening around you doesn't bother us or doesn't affect you because you aren't attached to any particular idea (or to a particular way of doing something.)
Ideal is the person who can make their body, mind or the relationships between them either substansive or insubstansive at will. Or they can find the balance point somewhere in between.
One of the ways that you can help your body to vary between substansive and insubstansive is to get better at sensing it and controlling it. One of the ways that you can help our mind vary between these two extremes is to notice the thoughts that you are thinking about. Once you notice the thoughts you are thinking you can choose whether you want to create a substantial connection or insubstantial connection to those thoughts.
One of the ways you can practice disconnecting from particular thoughts or from thinking is by being present. To be present you can focus on what you are doing. You can focus on using your senses-feeling your body, and you can focus on responding to what you sense-controlling our body. You thus become present.
By being present you can sense change as it occurs and You can respond. We can manage change and be simultaneous with it. You can create the change that you desire or allow it to happen.