Q1: Do you believe it when people associated with the I.P. (Internal Power) and "Aiki" phenomenon on this forum claim "it has to be felt" (IHTBF) in order to understand it?
Neither (see below)
Q2: Can you prove one way or the other if they are right or wrong about their claim that IHTBF?
No (see below)
Q3: Regardless of your answer to the previous question, please indicate how you can prove IHTBF right or wrong one way or the other: (select any that apply in order of preference -- delete any that do not apply)
There is no method. See below.
Q5. Do you have any other comments?
In re 1: I believe that when some people say that, they are convinced that it's true (and it may be).
I believe that when other people say so, they're repeating a platitude that they have not personally experienced to be true, but that sounds good. Not speaking of anyone specific, but this is the way of humanity. Suzuki roshi said a lot of things about Zen; and Joe Hyams said a lot of similar things, but the former was a Zen master, while the latter was a dabbler amusing himself with a popular fad.
In re: 2 and 3, it's not provable either way. If I fail to learn something by a more intellectual method, and then do learn it by "feeling" it, this doesn't prove that it has to be felt in order to understand it, or even that I had to feel it in order to learn it. All I've demonstrated is that feeling it is how I did learn it. You can't prove a negative, and you can't prove that no one, no where, could ever learn IPLMNOQ except by "feeling".