Though aikido movements may be taught with clear seemingly 2 dimensional movements sometimes, tonight I realized that in fact they are very 3 dimensional. This may be a strange way to explain it, but I was training with a new student tonight, and I found that he was doing the movements mostly correct, but nothing was happening. On the other hand, when I train with a senior student, as soon as I grab them or initiate the attack, throughout the whole technique I am put off balance and being thrown. Essentially, there should be a connection between uke and tori (throwee and thrower), and this is maintained by this 3D idea I have in my head.
Perhaps another example is in the simple same side single hand grab tenkan (movement) that we do at the beginning of every class. Essentially, you guide someone with your hand, but the meat of the technique is in your hips and waist. By sinking your weight and putting your hips at the center of the movement, your hand can easily guide the opponent, but if all you focus on is the hand, it's completely lost.