I prefer to defer to the founder.
O'Sensei didn't leave us completely dry on the subject. He defined the principles of triangle, circle, square on different occassion and you can find it in his written lectures (Saotome Senseis' book Aikido and the nature of harmony has a beautiful lecture regarding circle).
I find that when I do not have my own meanings for things I can keep my mind open to understanding the mystery of aikido as it is revealed. This does not mean I do not have operating understandings, it simply means I can rest from my meanings and opinions. This mind set has also served me well in accepting other learning levels and the learning levels of others.