On noticing this, the students became a bit concerned with how to separate seitei and koryu. Since they are similar, it’s easy to mix them together. This is a multi-level topic actually, so let’s deal with the easiest first. Don’t worry, beginners confuse the two, more advanced students don’t. You learn how not to eventually.
If you do two kata that are close to one another you need a cue to separate them. This might be shouting inside your head “do this one not that one” but you will eventually find small differences in how you initially move that will key in the responses of one or the other kata.
For our particular case we are dealing with Muso Jikiden Eishin Ryu and the Zen Ken Ren Iai. Many years ago one of my teachers went through a list of 24 differences between the first kata (Mae) of these two schools and I could probably still come up with that number. Fortunately, koryu is big, and you can actually get away with just four. From a koryu point of view, here’s the four you need. 1: grasp the tsuka left hand then right hand, not together. 2: do not shift the left knee forward when you lift the sword after the initial cut. 3: your left hand comes directly to your saya mouth when you start chiburi (rather than your obi at the hip) and 4: when you do chiburi (shaking the blood off) and rise up, the left foot comes immediately to the right (not after rising). These four points will distinguish our koryu mae from our seitei mae, but please note that number 3 is variable within different MJER lines, with some moving the left hand to the hip rather than the koiguchi.
So use the first difference here to cue yourself when doing mae, both hands at once to the hilt and your body goes into seitei mae, left hand then right and you go into koryu mae. Or back up and split them when you sit down. Seitei Mae is a fist to a fist and a half between the knees, koryu is two fists. Or look at the position of the hands on the thigh, or back up even further where the tsuka kashira of koryu mae is in the center of the body while the seppa is in the center for seitei. Pick whatever works for you and use that as your key.
This works for us, other koryu lines may or may not have those particular cues to use, so look at your own school and find something that suits. As I said, koryu is big, it can accomodate a lot of variation and can include doing the kata exactly as it is done in seitei. Really. What you need to avoid, in fact, is taking the koryu over to the seitei rather than worry about seitei in your koryu. Your koryu is between you and your sensei, there is no external standard, no grading, no authority which can impose standards. It is MJER until it is not, it is correct until it doesn’t fit the riai, then it is something else. Or it is MJER until it is named as a different thing (as in Muso Shinden Ryu). There is a continuous line between, say, uke nagashi of seitei, MJER and MSR (ryuto). Do the three one after another and you’ll see what I mean.
Eventually, as I just hinted, you might even get to the point where you really don’t care what the differences are since you’re more concerned with what the kata teach… but that’s quite a long way off, for now and the next several years you’ll be very concerned with “differences”.