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Anyone who while standing in a city street has looked up at the dome of the sky will recognize this figure as being the distillation of a fundamental condition of human life. On the one hand; order, sometimes man-made, sometimes natural, and on the other hand; boundless encircling space. On the one hand things as they appear to be, and on the other a space of unlimited possibility.
Circle Sky Heaven Infinite Non-manifest Essence Interior Cause All-Encompassing Center	Square Earth Earth Finite Manifest Things Exterior Effect Things Encompassed Four Directions

 

Those who drew the squared circle and who investigated its geometrical relationships found that the diagonal of the square seemed to have some importance as is shown in the following figure:

 

When early geometers came to try to understand mathematically the proportional relationship between the side of a square and its diagonal, they found that there was no straightforward way. Cut and divide as many times as you like, there can be no numerical relationship between the two. Today our system of numbers is able to describe the relationship as 1:1.414...(etc., a decimal without end...), but the two sides of the relationship remain incommensurable. We refer to the relationship as "irrational", not meaning "without reason", but "without numerical ratio".