Re: extension and ma-ai
I wrote recently in another thread about the danger of grasping: how, when faced with a challenge, our first instinct is to grab it as quickly as possible and to hang on as tenaciously as we can. I was speaking there about grasping in the literal sense, when dealing with uke's attack in aikido practice, but I think the danger also exists when dealing with non-physical challenges. Aikido training presents us with many new and sometimes startling things: there's this thing called maai, which your sensei no doubt explained to you in simple pragmatic terms just as Phi has: appropriate distance. But you sense that it's also connected to other things, so you try to grasp the concept of maai, to figure out exactly what it is, to give it labels and structures and boundaries, and then to try and formulate a framework for how it relates to this other thing, "extension". And in the process, maybe you add onto it a bit. Your sensei gave you a simple cottage, "maai" -- that looks too plain-Jane, so you give it gingerbreaded shutters and eaves and a fancy paint job and a deck out back with a hot tub. You build a new wing onto it, and a wing onto that, and six additional stories, and a golf course, and one day you're walking around your property and you see this old cottage and you say, "Damn that thing's tacky, let's just pull it down and put in a snack bar." And now, your roadside attraction...well, it's become the kind of thing of which a polite observer would say, "That certainly is something." But the original cottage is gone.
So, that's the danger of elaborating on a simple concept, and the world of aikido is fraught with it. That's not to say that I think the basic concepts of aikido don't have additional dimensions, or can't be thought of beyond their simplest literal meaning. But that's an understanding that can't come from books, and it can't come from the imagination, either. Our conceptual understanding of aikido has to rest on a foundation of practice -- we each need to accumulate our own personal empirical data, our own set of data points, for the conceptual understanding to be based on; otherwise, it's a house built on sand. Worst case, you come to love your "house", your theoretical "understanding", so much that when empirical data contradict it, you toss out the empirical data and cling to your own false construct.
So, in summary, I think it's best to be cautious about creating some Unified Field Theory of All Aikido Concepts. At their foundation, maai is just appropriate distance and extension is just a mechanical description for a type of movement. If they have other meanings as well, that's fine, but any authentic (non-forced, non-contrived) meaning will reveal itself through practice. Practice won't lead you wrong; theorizing might. Trying to grasp aikido concepts in a hurry is just like reaching up to grab that shomenuchi, because you've got to do ikkyo and time's a-wastin'. At best it ends in a schoolin', at worst it ends in self-deception and ultimately in tears.