Lately I've been harping on the benefits of adding a practice knife to your regular practices. Note that I'm not talking about spending a lot more time emphasizing knife defenses - the very concept of martial arts knife defense is probably greater than 95% B.S. The only reliable defense against a knife attack is avoidance...
I'm talking about some collateral benefits to adding a knife to your practice. Just having either the attacker or the defender (or sometimes both) holding a knife changes your practice and adds a lot in a couple of ways.
- It teaches you how to move and hold and use sharp objects, so maybe you'll be less likely to kill yourself while running with scissors.
- Even if uke is not actively attacking with the knife, the blade absolutely screams at tori, "PAY ATTENTION TO ME!"
So, uke is learning how to move around in complex ways without cutting himself up, while tori is learning to move in a free and flowing manner while constrained by one thing and while paying attention to a second thing.
A great example is the set of 8 wrist releases that we learn as beginners and that we review every class. These 8 movements involve uke stepping into ma-ai and taking a hold of one of tori's wrists. Face it, a wrist grab is not the most realistic or threatening attack in the world - but they are perfect for beginners to start learning movement and principle.
Problem is, after you're about brown belt or so, it's easy to feel like you've got a pretty good handle on wrist releases and they become just another boring thing that sensei makes us do for warm-up before we get to the real learning in each class. It is easy to get complacent and lax and let your attention wander during releases.
But then uke grabs a practice blade in his free hand, and all of a sudden the blade screams at tori, "HEY! LOOK HERE! DANGER WILL ROBINSON!" but tori still has to be able to move around the constraint that uke is imposing on him through the wrist grasp.
Tori is learning in these releases to put some of his attention on the knife while still moving within/around constraints.
Tori is also learning another of the most vital lessons in aikido - one of the foundations for everything - that all ukes are deadly dangerous. If uke is able to touch you then he is able to kill you. Keeping this in mind helps tori to learn to use taisabaki and kuzushi to disarm uke by removing his opportunity and ability to touch you with the knife. Having uke carry a knife in his free hand helps tori to keep this lesson in the forefront of his mind during practice.