The nice thing about this mathematical controversy is that everyone can understand it.

Τ (tau) equals Π times two. The circumference of a circle is 2Πr where r is radius of that circle, so it also equals Τr. Another way to express this is Πd where d is the diameter, or alternatively Τd/2 . These formulae are ratios.

Here’s what they’re arguing about. A circle is a real thing. The ratios mentioned above express, perhaps, something about the fundamental nature of reality. Putting the number ‘2’ in any of them is a bodge to get the result right. It would be better to have a formula that didn’t have a number in it. Two versions of such a formula are available: Πd and Τr.

This raises the question, which is the more fundamental measurement of a circle, the radius or the diameter? If a circle is defined as the set of points a common distance from a given point, the centre, then the fundamental properties of a circle are the position of the centre and the radius. If you take an abstract circle with no set position but just its size, the only property is the radius.

That’s what the Taoists are arguing: the radius is the measurement that should be used and so children should be taught to multiply it by Τ, instead of using Π.