ian

Saito shows in one of his videos how someone with a knife (blade prtruding from little finger end) produce nikkyo on nage when you attempt ikkyo; blade goes over nages wrist to the outside.

Goykyo prevents this - however I think it is mechanically slightly worse as the thumb rather than the hand may get more pressure from the downward attack (thumb being weaker) if you are not careful or blending well.

Also gokyo tends to be done with the blade to your left slightly - by directing with non grabbing hand (so you are not underneath it and thus get don't killed if you miss). If you do this with ikkyo it is weaker and it often exposes your rib cage beneath the grabbing hand (since it produces something more like a karate block).

Practically, 60% of people attacked with knives don't realise until after the attack. Also, any skilled knife-fighter will conceal the weapon and probably strike you first with their other fist (or grab you). Thus I hate to seperate weapon from unarmed responses (aikido rarely does seperate them).

Although ikkyo and irimi-nage (I believe) are the very core of aikido, all the techniques are part of one whole. Removing it would be like removing kokyu-nage. From something like a shoulder grab, it can sometimes be more convenient to go for a nikkyo, but if the arm locks out and the hand releases this can easily flow into a gokyo.

I certainly think all the individual technique practise is just so we don't get shocked when the techniques spontaneously appear from free-style (blending) aikido practise.