The opening Koan from the venerated Mumonkon Collection so central in Japanese Rinzai Zen, is: ‘Joshu’s Mu!’. It is in response to the question: ‘Does a dog have Buddha-Nature?’.
Joshu’s ‘Mu!’ is a negative particle, a vociferous assertion of negation. The driving kinetic of its terse formulation is its simultaneous self-consumption.
‘Mu’ is a Self-Eating Expression.
Mumonkon [1228 CE]; ‘The Gateless-Gate’; the title itself, a contradiction.
Mu, is the single most used character in the entire Chinese Buddhist canon. Zen was the first formal teaching tradition to use Absurdity as an active tool through its Koan culture. Others flirted with it but never saw its significance; and if they did, were too needy of conventional respectability to let it display.
See the later Posts on Absurdity and its root in the Empty Class of Classical Logic. [I am not sure the Posts are up yet; I’ll remind myself to place a link once they are up.]