What I do see on this forum are many statements that are quite vague about what IP / IS is or how to attain it.....
OK, fair enough, I am going to throw this out for what it's worth - it is my view on things and not necessarily how others that are studying IP/IS look at things.
I like to look at it this way:
IS - Internal Strength or Internal Skill? I think both terms can be used when discussing what we are doing - so, I think I will differentiate by IStr for strength and ISkl for skill.
ISkl - I see internal skill simply as a label depicting some level of Internal strength and/or power.
IStr - I see internal strength as a quantified capacity of a potential internal force; i.e. How strong are you, etc.
IP - I see internal power as a quality of use of an internal strength force. As in the formula Power = force (strength) times acceleration (speed) in other words, a less strong but faster person can delivery more power than a slow strong person. IMO, there are many forms and levels of IP with Tohie's Ki tests being on a lower level and Takeda's AIKI being on a very high level.
AIKI - as mentioned above, I see AIKI as a high level form of IP - it is the joining of opposing forces (in/yo, yin/yang) within the body to establish internal balance in a static as well as a dynamic state.
In summary, we are working on increasing our ISkl by developing our IStr to be manifested by IP via the AIKI methodology. Simple, right? - let's break it down a little. First we need to develop a body ready for AIKI, we do that by training for internal strength and internal power. These are two different things, and as in the development of external muscle strength and muscle power, there are different activities for each development. In the internal strength model, you need to develop a strong connected body that is instant on with the transmission of energy to all parts all the time; this is where the capability of having one thing moves, all things move comes from. The solo exercises we do for this are the ones that get our fascia, ligaments, and tendons more engaged and moving together. Next we need to develop internal power so you can do something with the internal strength/force - as mentioned, power is a quality that utilizes the strength/force; where the most prevalent quality is acceleration/speed. This is where the exercises we do that focus on flexibility and range of movement come in. Then, we take that AIKI ready body and apply the attributes of the AIKI model to direct the internal activities required for the use and manifestation of soft power.
Anyway, just the way I like to categorize the various aspects of what we are doing and bring them all together to provide the functions we are trying to accomplish - of course, other views may be different.