O-Sensei was fond of saying that the foundation of aikido is based on 3 fundamental geometrical shapes; Circle, Square, and Triangle. What do these shapes have to do with our aikido training? O-Sensei made both literal references (citing the Kojiki and other mythical and mystical sources) and symbolic references that were often open to wide interpretation.
These shapes find their source, in both Buddhism and Shinto beliefs, as the Sangen, the Three Eternal Origins. Sangen has varied esoteric symbolism depending on the specific sources but Sangen is sometimes referred to as Mind, Body, and Spirit, manifested as hi.fu.me, where Hi is Breathing in (the breath of the earth (yin)), Fu is breathing out (the breath of heaven (yang)) and Mi is the Unifying Bridge or Floating Bridge of Heaven which binds (musubi) heaven and earth and is described in the ancient creation myths.
O-Sensei said that Aikido is “Standing on the Floating Bridge of Heaven”. These kinds of mystical references usually left even his most serious students confused and bewildered.
"In the Way, you must first stand on the Floating Bridge of Heaven. If you do not stand on the Floating Bridge of Heaven then Aiki will not come forth." - O-Sensei
"Aikido is the Way and Principle of harmonizing Heaven, Earth, and Man." - O-Sensei
In this photo O-Sensei demonstrates uniting heaven and earth, manifesting aiki with his aiki-jo, while standing on the floating bridge between heaven and earth. Heaven (Fu) - Man (Mi) - Earth (Hi)
How does all this relate to the Circle, Square, and Triangle of Aikido?
Triangle (Iku musubi): The energizing fundamental, it is the dimension of ki-flow symbolizing initiative. The triangle is the key to entering and interrupting the flow and direction of an attack. Entering (irimi) iku musubi as is striking (atemi). Circle (Taru-musubi): The completing fundamental, is the dimension of liquid symbolizing unification. The circle is the key to blending and harmonizing the flow of energy between attacker and defender. This include turning (tenkan) to the rear (ura) and to the front side (omote). But it also represents the 3-dimensional circles (spheres and spirals) that found in every aikido technique to take the balance and throw. Square (Tamatsume-musubi): The fulfilling fundamental is the dimension of solidity symbolizing form. The square is the key to controlling and grounding of ones power through an opponent. The square allows us to absorb and ground our opponent's power without being knocked over and to pin our opponent with the weight of the earth. In the words of O-Sensei; "Enter in the sign of the triangle, perform the body movement (tai-sabaki) of the technique as a circle and control in the sign of the square." "The body should be triangular, the mind circular. The triangle represents the generation of energy and is the most stable physical posture. The circle symbolizes serenity and perfection, the source of unlimited techniques. The square stands for solidity, the basis of applied control." Just a few symbolic characteristics of the Circle, Square, and Triangle
Triangle
Man
Irimi (Entering)
Stars
Truth
Gas
Circle
Heaven
Tenkan (Turning)
Moon
Virtue
Liquid
Square
Earth
Fudoshin (Immovable spirit and grounding)
Osae Waza (Pinning)
Sun
Will
Solid
Great! How do I use this in my aikido training? Here's an example of just one practical way to think of these shapes in your daily practice. You are standing, relaxed and grounded (square). You assume the hanmi posture (a triangle orientation of your feet and your hands) to permit irimi (triangle) movement. Your opponent attacks and you enter (irimi) to receive the strike and blend with the attack using tenkan (circle) and finally apply ikkyo (first technique) using a circle (that receives, rises, goes out, drops and returns to you). Finally, you solidly pin your opponent (osae waza) by binding your opponent, through you, to the earth (square). It may be fun and inciteful for you to imagine practical aikido applications of the three shapes (Triangle, Circle, Square) in your own training.