Edward raises an interesting question. What makes Aikido "hard"? Is it how hard Uke hits the mat? Is it how much Uke resists? How hard Nage is working? Is it the force of the attack? If Uke never resists but takes Ukemi until they get the dry heaves are they practicing hard or soft? If you go to the dojo every day and your buddy only makes it twice a week are you practicing harder than he is?
Anyway, you can see what I'm getting at.