Many people hear the word harmony, as well as those of helping your attacker, and assume that harmony means using less force and more control when in that situation.  Using less force is NOT using harmony.  Think of the Yin Yang symbol, and understand that this is a perfect realization of harmony.  Black pushing white, white pushing black, everything equal, all in a perfect balance.  If we see black as the attacker and white as the defender, then as soon as the attack was started it would be impossible to tell that black had instigated the conflict.  Now assume that black is still attacking, but that white is using the idea of [Harmony=less force] and see what happens.  As the two circle around, black will slowly start to overwhelm white, gaining a bit of control at every rotation, until eventually white will be completely gone, and the entire circle will be black.  Harmony is the idea of equal force, meaning that the harder or faster the attack, the harder and faster the defense.  The harder black pushes, the harder white pushes, but EQUALLY!!!!  The fact that you are defending does not give you the control to change the speed you should do the technique, it should be exactly the same speed as the attack was so that there is no jerking motion, which causes your attacker to not even be aware that something went wrong in his attack until it is too late.  White MUST NOT push harder than black, because white will soon dominate the circle, and that's not what Aikido's about.  The forces must be kept equal so that balance my be kept.  In physics this is stated as:  "The amount of positive energy in the universe is exactly equal to the amount of negative energy; the universe is, and always has been, a perfectly balanced energy system."

I have talked about the idea of harmony, about protecting your partner, but is it possible that there could be a time when we should not concern ourselves with our partner's safety?  The idea of Harmony and helping your opponent is ideal, but there is a condition.  If your attacker is using a weapon, a Tanto (knife), Katana (sword), or anything else, this should be considered a Life-or-Death situation, and we have to concentrate on getting out alive more than helping our partner.  Once the weapon is not being used, then we can try to help him.  Weapons are very serious, obviously.  Messing up a technique and getting punched is of course uncomfortable and painful, but odds are you're going to live.  Even a minor wound from a weapon can be very serious, and we must treat it as such.  When someone punches at you, they are angry, aggressive, but they're probably not intending to kill you.  With a weapon, your life is in danger.  Weapons are used to kill, and this must be thought of when attacked by one.  Your only priority must be to disarm your attacker, and only after this has been accomplished should you concentrate on controlling the technique to protect your partner.