Zen is rational, but it is not linear and it is not bound by logic.
Can you possibly elaborate? How can Zen be rational if it is not bound by logic or reasoning?
Zen relies upon Buddha Nature directly. Because Buddha Nature cannot be elaborated upon meaningfully using logic, Zen is beyond logic. Logic is a tool for consistent reasoning but Zen accords to the circumstance and condition. Zen's rationality is totally based on Buddha Nature. You can reason correctly in Zen, just not with a linear intellectual approach (although you can get started that way).
_________________Kirt's Tibetan Translation Notes
"Only you can make your mind beautiful."
HH Chetsang Rinpoche