Cassia Rose Heatley
So in general, I think it can be quite a frustrating topic to discuss aiki, it is at best elusive and hard to prove effective. I mostly consider it as something like faith, if it improves people for the better I am all for it. Very few people claim to "possess" aiki and I have never had the experience to train with someone who does so. It's a little like trying to grab smoke, everyone has a perspective on what they think it is like or how much importance it has, but it is not tangible enough to be properly defined and outlined.
As you can see, there's no universal agreement in the Aikido world at large as to what "aiki" actually is. However, the "aiki" talked about by Cady, Budd, etc. is a fairly specific thing.
This is one of those things that fall under "IHTBF" - It Has To Be Felt. It is quite tangible, but can be best understood by physical contact. Trying to understand by reading about it or watching videos that purportedly display it - without the prior physical contact experience - doesn't seem to work for most people.
Budd can show you how it feels, and also teach you how to do it in short order. There are a few others out there who can as well.