State of Matter...
Katai (rigid), or Kihon(basic), executed when you receive an attack static (grabbed firmly), and there is no attempt to evade it.
Ki No Nagare (flowing), executed in motion. You don’t wait for the attacker to grabb, but start merging into his movement before contact is made.
Ki (spirit), the ultimate Aikido technique.
“Aikido is generally believed to represent circular movements. Contrary to such belief, however, Aikido, in its true KI form, is a fierce art piercing straight through the center of opposition". -Morihiro Saito-Sensei (Traditional Aikido, Vol. 5)