Mary, I was in no way trying to disparage your use of the phrase but to explain that I thought that, in fact, it was your shorthand for a whole lot of pretty specific stuff....which is pretty much what you have just said yourself.
My reasoning was based on coming from a dojo in Tohei Sensei's lineage - I came to view his 4 principles as a shorthand for a whole lot of specific body/brain things that can be specifically taught and practiced, whereas I have seen that merely telling the 4 principles to beginners doesn't give them anything they can use.
Does that make more sense?
Pardon the recently-tested-for-6th-kyu interjection.
Maruyama-sensei was Tohei's student as far back as Hombu and through the formation of Ki Society before Maruyama spun off Kokikai. We still have the Four Principles with one difference - at some point, Maruyama changed the wording of the fourth one from "Extend Ki" to "Develop your positive mind". He believed these meant pretty much the same thing but the altered version was a clarification. His formative experience partly involved being one of the early teachers in the USA, where people were less inclined to accept things on authority alone.
I wish I could find the article again to link to, but there was a college paper that quoted Maruyama-sensei speaking at a Fall Camp some years ago, where he expressed the opinion that ki was "correct feeling". We don't use the term in class here, but explaining it that way made sense to me from the student perspective.
Bear in mind: I'm an extremely secular person. I look with suspicion and disdain on anything that smacks of magic or mysticism. I don't find "ki" to be a useful term for me as a student because it seems no one can agree on what it means. What I can understand are thought processes and body mechanics, and when someone at my dojo speaks of "extending ki" I can translate it into this context.
But to try to tie it all together, ki test 101: unbendable arm. Positive mind: your body will follow your attention, your focus, your imagination. I am relaxed, but not floppy. I focus on imagining the "firehose" feeling, and the muscles respond in the correct way - one day someone will do all the biomechanics research to establish exactly what's happening, but it's enough for me to know that I can do it easily, reliably, and that it's not a trick. The thought process is positive mind, and the result is correct feeling.
Of course if this were all to it, we wouldn't need the dojo. You learn, gradually, how unbendable arm, ki exercise warmups and all those other things apply to the rest of Aikido. It's one thing to have correct feeling, or keeping focus on one point, when sitting or standing comfortably, and a very different thing to maintain it when throwing or being thrown. That's what practice, and the other principles are for.
That's my interpretation, subject to evolve with experience. I know others will disagree and I've seen the fights that break out on the subject, something I'd rather avoid.
But I hope it was clear enough to be understandable.